Our Astro-Chemical History Past, Present, and Future Sept. 10-14 2018 Assen, The Netherlands

Abstract Book

Program Monday 12:30-14:00 Lunch 14:00-15:25 14:00 Welcome and logistics 14:10 Summary of activities/results from the Action (Laurent Wiesenfeld) 14:40 The Future of Astrochemistry - Farid Salama (NASA) 15:25-16:00 Coffee break 16:00-17:30 Formation of COMs: surface routes vs new gas-phase routes 16:00 Audrey Coutens (Bordeaux, FR) 16:30 Dimitrios Skouteris (Pisa, IT) 17:00 Alexey Potapov (University ofJena, DE) 17:30-18:30 Welcome reception/posters 19:00-20:00 Dinner Tuesday 9:00-10:30 Low temperature chemistry and kinetics and processes (gas & solid) 9:00 Sergiy Krasnokutskiy (Jena, DE) 9:30 Johannes Kästner (Stuttgart, DE) 10:00 Stanka Jerosimić (Belgrade, RS) 10:30-11:00 Coffee break 11:00-12:30 Isotopic fractionation pathways in space 11:00 Kenji Furuya (Tsukuba, JP) 11:30 Eva Wirström (Chalmers, SE) 12:00 Olli Sipilä (Helsinki, FI; MPE, DE) 12:30-14:00 Lunch 14:00-15:30 Nanoparticles: Condensation, reactivity and diffusion 14:00 Herma Cuppen (Nijmegen, NL) 14:30 David Gobrecht (Leuven, BE) 15:00 Antoni Macià Escatllar (Barcelona, ES) 15:30-16:30 Coffee break/poster session 16:30-18:00 16:30 Chemistry of Planetary Atmospheres - Christiane Helling (St Andrews, UK) 17:15 Comet chemistry - Kathrin Altwegg (Bern, CH) 19:00-20:00 Dinner Wednesday 9:00-11:00 Hydrocarbon chains and rings in space 9:00 Ricardo Urso (INAF, IT) 9:30 Maria Luisa Senent (CSIC, ES) 10:00 Thomas Pino (ISMO Paris, FR) 10:30 Sandra Wiersma (Amsterdam, NL) 11:00-11:30 Coffee break 11:30-12:50 WG summaries 11:30 WG2 - Icy Grain Surface Chemistry - Dmitry Semenov (Munich, DE) 11:50 WG4 - Isotopic Fractionation - Charlotte Vastel (Toulouse, FR) 12:10 WG3 - UV and X-ray Photochemistry - Jean-Hugues Fillion (Paris, FR) 12:30 WG1 - Chemistry in Cold Diluted Gases - Octavio Roncero (Madrid, ES) 12:50-13:30 Lunch 13:45-19:30 Social Event 14:00-16:00 Free Time Giethoorn (puntertocht) 16:30-18:30 MC Meeting (with coffee) 19:30-21:00 BBQ (outside, weather permitting)

2 Thursday 9:00-10:30 Challenges for astrochemical modeling 9:00 Marcelino Agúndez (Madrid, ES) 9:30 Serena Viti (London, UK) 10:00 Wing-Fai Thi (MPE, DE) 10:30-11:00 Coffee break 11:00-12:30 Challenges for astrochemical modeling (continued) 11:00 David Trunec (Masaryk, CZ) 11:30 Jean-Christophe Loison (Bordeaux, FR) 12:00 Ewine van Dishoeck (Leiden, NL) 12:30-14:00 Lunch 14:00-15:00 Pop up poster talks 2-3 min for each poster, one slide maximum 15:00-16:00 Coffee break/poster session 16:00-17:30 High energy chemistry (VUV, Xrays and electrons) 16:00 Christian Rab (Groningen, NL) 16:30 Vera Mazankova (Brna, CZ) 17:00 Christian Alcaraz (Saclay, FR) 19:00-20:00 Dinner Friday 9:00-10:30 Optical and spectral properties of solids in space 9:00 Jennifer Noble (Lille, FR) 9:30 Anita Dawes (OU, UK) 10:00 Belen Mate (CSIC, ES) 10:30-11:00 Coffee break 11:00-12:40 The Future 11:00 New Experimental Directions - Ian Sims (Rennes, FR) 11:30 Molecules at high redshift: from ALMA to SKA - Jeff Wagg (SKA, UK) 12:00 The future of surface chemistry - Stephanie Cazaux (Delft, NL) 12:30 Final Remarks 12:40-13:30 Lunch 13:30/14:00 Bus (organized) directly to Schiphol airport

3 List of Posters

Stefano Antonellini Deuterium Chemistry in Interstellar and Circumstellar environments: A step towards a full spin chemistry

Jo˜aoBrand˜ao The OH + CH3OH → CH3O + H2O at low temperatures: a barrierless process

Henda Chaabouni Thermal desorption of NH2CHO and CH3NH2 from HOPG and ASW ice surfaces

Qiang Chang The Chemical Evolution from Prestellar to Protostellar Cores: A New Multiphase Model With Bulk Diffusion and Photon Penetration

Pablo del Mazo Dynamics for the H2CO + OH reaction

Marcin Gronowski Accuracy of spectroscopic constants predicted by explic- itly correlated coupled cluster methods

Inga Kamp Planet forming disks: Challenging astrochemical labora- tories

Jennifer Noble Photochemistry of PAHs embedded in water ice: new in- sights into the role of ice structure on the reactivity and ionisation energies of PAHs

Gunnar Nyman On the gas-phase formation of the HCO radical: accurate quantum study of the H+CO radiative association

Pilar Redondo Hydrogenation of Isocyanic acid on Water Ice Surfaces: a Computational Approach

Dmitry Semenov Sulfur-bearing species as tracers of protoplanetary disk physics and chemistry

Christopher Shingledecker Solid-Phase Cosmic Ray-Driven Radiation Chemistry in Astrochemical Models

Ionut Topala Interstellar carbon dust analogs obtained using plasma based processes

Joanna Zapa la Absolute intensities and photolytic behaviour of ethyl mercaptan (HS-CH2CH3) and dimethyl sulfide (CH3-S-CH3) in Ar and in CO

4 Talks The Future of Astrochemistry

F. Salamaa

aSpace Science and Astrobiology Division, NASA Ames Research Center, Moffett Field, California, USA Contact: [email protected]

An overview of the current status and critical needs in astrochemistry will be presented. The discipline of Astrochemistry is an overlap of astronomy and chemistry and is com- monly defined as the study of molecules in the Universe. Molecules are one of the vital ingredients of our Universe and the understanding of their interaction with photons and cosmic ray radiation in space is key to our understanding of the evolution of the Universe. Astrochemistry sheds light on the chemistry of interstellar clouds and the formation of stars and planets and applies to both the Solar System and the interstellar medium. As a result, Astrochemistry includes gas-phase chemistry, ices, surface chemistry, photochem- istry, isotope chemistry and plasma chemistry among others. Emphasis will be given in this presentation to the major role that astrochemistry plays in the optimization of the science return from space missions.

6 Exploring the formation of complex organic molecules in solar-type protostars with ALMA

A. Coutensa, J. K. Jørgensenb, H. S. P. M¨ullerc and the PILS team

aLaboratoire d’Astrophysique de Bordeaux, Univ. Bordeaux, CNRS, France bCentre for Star and Planet Formation, Niels Bohr Institute & Natural History Museum of Denmark, University of Copenhagen, Denmark cI. Physikalisches Institut, Universit¨atzu K¨oln,Germany Contact: [email protected]

Complex organic molecules are detected in a large variety of astrophysical environments. They are particularly abundant in the warm inner regions of protostars, where planets, comets and asteroids are expected to form. These molecules may survive during the star formation process and be incorporated into asteroids and comets, which could deliver them to planetary embryos through impacts and thus favor the emergence of life. It is, therefore, important to understand how these molecules form and how they evolve towards more complexity. Thanks to the high spatial resolution and high sensitivity of the interferometers ALMA and NOEMA, new opportunities were offered to astronomers to characterize the molecular complexity in low-mass star-forming regions. In particular, several new detections of complex molecules were obtained in the framework of the PILS program, an unbiased spectral survey of the solar-type protostar IRAS 16293-2422 with ALMA (e.g., Jørgensen et al. 2016, Lykke et al. 2017, Ligterink et al. 2017). Isotopologues of several complex molecules (D, 15N, 13C) were also detected for the first time in the interstellar medium (e.g., Coutens et al. 2016, 2018, Jørgensen et al. 2016), which helps constrain formation pathways of molecules. In this talk, I will especially mention the recent detection of cyanamide (NH2CN) and its deuterated form (Coutens et al. 2018). I will discuss what it teaches us regarding its formation in connection with formamide (NH2CHO) and why it would be interesting to search for its 15N isotopologues. References : Coutens et al. 2016, A&A, 590, L6 • Coutens et al. 2018, A&A, 612, A107 • Jørgensen et al. 2016, A&A, 595, A117 • Ligterink et al. 2017, MNRAS 469, 2219 • Lykke et al. 2017, A&A 597, A53

7 Formation mechanisms of prebiotic molecules in the interstellar medium

D. Skouterisa, V. Baronea, N. Balucanib, C. Puzzarinic, C. Ceccarellid, F. Vazartd

aScuola Normale Superiore, Pisa; bUniversit`adegli Studi di Perugia; cUniversity of Bologna; dInstitut de Planetologie et d’Astrophysique de Grenoble

The search for the origin of prebiotic species in space is an ongoing discipline of enormous interest in astrochemistry and in the study of the origin of life. It has been shown that essentially all biological macromolecules can be envisaged as forming from relatively simple precursors, such as formamide, which are relatively common in interstellar clouds (ISCs). Yet, the formation of formamide and other simple prebiotic molecules is difficult to explain in the harsh environments of ISCs, where very low temperatures and number densities prevail. Dedicated experimental approaches have been developed to address prebiotic molecules formation mechanisms, in which either the low temperature or the low number density regimes are reproduced. Nevertheless, for some specific cases, the experimental techniques are difficult (if not impossible) to apply. For this reason, we have started a systematic investigation by using high-level electronic structure calculations coupled with kinetics cal- culations to elucidate the mechanisms of formation of complex organic molecules (COMs) of prebiotic interest which cannot be addressed experimentally. The mechanisms dis- cussed take place exclusively in the gas phase, starting from reactants which are rela- tively abundant in ISCs. The species discussed include formamide (a possible precursor of both aminoacids and nucleobases), glycolaldehyde (a prototype for sugars), acetic acid (a possible precursor of glycine) and formic acid. Dr. D. Skouteris wishes to thank the COST Action CM1401 ”Our Astrochemical History”, the Italian Ministero dell’Istruzione, Universit`ae Ricerca (MIUR FFABR17 SKOUTERIS) and the Scuola Normale Superiore (SNS RB SKOUTERIS) for financial support. References: 1. V. Barone, C. Latouche, D. Skouteris, F. Vazart, N. Balucani, C. Ceccarelli, B. Lefloch GAS PHASE FORMATION OF THE PREBIOTIC MOLECULE FORMAMIDE: IN- SIGHTS FROM NEW QUANTUM COMPUTATIONS, MNRAS Letters, 453, 1, L31 (2015). 2. D. Skouteris, F. Vazart, C. Ceccarelli, N. Balucani, C. Puzzarini, V. Barone NEW QUANTUM CHEMICAL COMPUTATIONS OF FORMAMIDE DEUTERATION

8 Formation of molecules on the surface of laboratory interstellar grain analogues

Alexey Potapov

Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Germany Contact: [email protected]

An understanding of possible scenarios for the formation of astrophysically relevant molecules, particularly complex organic molecules (COMs), will bring us one step closer to the un- derstanding of our astrochemical heritage. Studying the formation of COMs is crucially important to understand the processes that lead to stars and planets formation, and to understand a degree of molecular complexity on planetary bodies, which can shed some light on the origin of life on Earth. Interstellar ices covering dust grains are known to be a source of COMs detected in the ISM, which cannot be created via gas phase reactions. The main triggers of grain surface chemistry in the ISM are UV irradiation, cosmic rays, thermal processing, reactions with radicals, and atom addition. Many laboratory experiments have been performed on the formation of simple and com- plex molecules, including amino acids, in interstellar ice analogues using the triggers mentioned above. However, a major part of the laboratory work deals with molecular ices covering standard substrates not related to the ISM, such as metals, KBr or HOPG. The grain surface can participate in ice chemistry and can alter the efficiency of molecule formation, but there is a handful of works on the formation of molecules in dust-ice sys- tems. Only CO and CO2 have been synthesized in laboratory interstellar dust-ice grain analogues up until very recently, when we performed our experiments on the formation of formaldehyde on hydrogenated fullerene-like carbon grains by O/H atom addition. The formation of H2CO is an indication for a possible methanol formation route in such sys- tems and CH3OH, in turn, is well-known as a starting point toward the formation of more complex organic molecules in the ISM. Thus, an alternative route of COMs formation in the interstellar medium, grain surface processes, has been probed experimentally.

UV irradiation Atom bombardment

O2 Heat OH HO2 H Cosmic rays

Dust grains NH3 CO2

CO

CH4

CH3 OH

4

Figure 1: Schematic figure showing cosmic grains covered by molecular ices and the main routes of interstellar ice processing that takes place in astrophysical environments

9 Formation of organics and fullerene polymers via C atom addition

S.A. Krasnokutskia, M. Goulartb, A. Kaiserb, T. Henningc, A. Ritschb, C. J¨agera, D.K. Bohmed, P. Scheierb

aLaboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena, Germany bInstitute for Ion Physics and Applied Physics, University of Innsbruck, Technikerstrae 25, A-6020 Innsbruck, Austria cMax-Planck Institute for Astronomy, Knigstuhl 17, D-69117 Heidelberg, Germany dDepartment of Chemistry, York University, 4700 Keele Street, Toronto M3J 1P3, Ontario, Canada Contact: [email protected]

Two different types of experiments are presented. In the first part we report the out- 1 come of sequential encounters of C60 with C atoms in cold environments. It was shown that C addition at low temperature enhance the chemical activity of the surface of C60 by carbene formation. The latter may pave the way toward a generation of a new class of fullerene derivatives. Reactive C60 carbene species may also be formed in in- terstellar and circumstellar environments containing C and C60, where they could add H2 and H2O, as well as C60, to form derivatized fullerene molecules such as C60(CH(H))n, C60(CH(OH))n,C60(C=CO)n, and even C60(C=C60)n. Interestingly, the 3D fullerene polymer film formed via such reactions has an IR absorption spectrum very similar to that of bare C60 molecules. This raises the question on the assignment of the observed emission bands to the monomeric molecules. Low-temperature reactions on the surface of cosmic solid particles (dust) are thought to be responsible for the formation of complex organic molecules observed inside dark molecular clouds and planet-forming disks. In our experiments, we tried to mimic the condensation of carbon on dust. The condensation of C atoms together with the most abundant in- terstellar molecules (H2,H2O, and CO) was studied. The reaction C + H2 → HCH is a key reaction in the formation of complex organic molecules (COMs). This reaction was found to be barrierless, which is in contrast to an energy barrier of 2500 K considered in 2 all chemical reaction databases. Therefore, the observed rapid low-temperature C + H2 surface reaction dramatically change the complete carbon chemistry network. The COMs were found to grow via the addition of C atoms, where the initial step is represented by the reactions C + H2 → HCH, HCH + CO → OCCH2. The growth ends up with the formation of organic carbon containing a large fraction of oxygen.3 Therefore, the condensation of carbon in low temperature areas of the ISM could partly or even fully explain the observed depletion of oxygen.

1S. A. Krasnokutski, M. Kuhn, A. Kaiser, A. Mauracher, M. Renzler, D. K. Bohme, and P. Scheier, J. Phys. Chem. Lett. 7 (2016) 1440. 2S. A. Krasnokutski, M. Kuhn, M. Renzler, C. Jger, T. Henning, and P. Scheier, Astro- phys. J. Lett. 818 (2016) L31. 3S. A. Krasnokutski, M. Goulart, E. B. Gordon, A. Ritsch, C. Jger, M. Rastogi, W. Salvenmoser, T. Henning, and P. Scheier, Astrophys. J. 847 (2017) 89.

10 Hydrogen Transfer Reactions of Interstellar Complex Organic Molecules

V. Zaverkin,a S. Alvarez-Barcia,´ a T. Lamberts,a,b J. K¨astnera

aInstitute for Theoretical Chemistry, University of Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany; bcurrent address: Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502, 2300 RA Leiden, The Netherlands Contact: [email protected]

Hydrogen addition and abstraction reactions play an important role as surface reactions in the buildup of complex organic molecules in the dense interstellar medium. Addition reactions allow unsaturated bonds to be fully hydrogenated, while abstraction reactions recreate radicals that may undergo radicalradical recombination reactions. We calculated rate constants for many surface-bound reactions involving glyoxal, glycoaldehyde, ethylene glycol, methylformate, but also propynal, propargyl alcohol, propenal, allyl alcohol, and propanal. We used quantum chemical methods with instanton theory that takes nuclear quantum effects like tunneling into account inherently. Our results are in good agreement with and can explain the observed experimental find- ings. The hydrogen addition to the aldehyde group, either on the C or O side, is indeed slow for all molecules considered. Abstraction of the H atom of the aldehyde group, on the other hand, is among the faster reactions. Furthermore, hydrogen addition to C-C double bonds is generally faster than to triple bonds. Preliminary work on the radical recombination of the three fundamental radicals (HCO, CH2OH, CH3O) mentioned above, indicates that although radical-radical reactions are proposed to be barrierless, not all possible product channels are likely.

S. Alvarez-Barcia,´ P. Russ, J. K¨astner,and T. Lamberts, 2018, MNRAS, 479, 2007

V. Zaverkin, T. Lamberts, M. N. Markmeyer, and J. K¨astner,2018, A&A, DOI 10.1051/0004-6361/201833346

Figure 1: Schematic representation of some of the reactions covered.

11 Can Anions of Cyanopolyynes be stable in Astrophysical Environments

S. Jerosimi´ca, F. A. Gianturcob, R. Westerb

aFaculty of Physical Chemistry, University of Belgrade, Studentski trg 12-16, PAC 105305, 11158 Belgrade, Serbia; bInstitut f¨urIonenphysik und Angewandte Physik, Universit¨at Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria Contact: stanka@ffh.bg.ac.rs

Carbon chain molecules Cn,H2Cn,CnN, HCnN, and some of their anions have been astronomically observed, with the cyanopolyyne HC11N as the largest straight-chain interstellar molecule (for a recent review see e.g. [1]). In this presentation we discuss − the possibile existence of stable HCnN cyanopolyyne anions (with n = 1, 3, 5,... ) in the astrophysical environments where the corresponding neutrals were already detected. Further, we analyze their possible role in providing efficient paths to the formation of the carbonitrile CnN− anions, which are also detected in the Molecular Clouds and the Circumstellar Envelopes of the ISM. The possible reactions with the title anions are proposed:

Electronic states and electron affinity values of corresponding neutrals were cal- culated by using ab initio structural calculations (applying coupled cluster and density functional theory methods in MOLPRO 2012.1 package [2]). Our findings suggest that the neutral cyanopolyynes can have two types of stable anions by either forming slightly distorted non-linear structures of Valence Bound States (VBSs), or more weakly bound dipole-bound states (DBSs) at the neutral linear configurations. Calculations of anionic H-bond stretching indicate that the CnN− species can be formed by following the breaking − of the terminal C-H bond in the stabilized anionic HCnN complexes. Keywords: astrochemistry; cyanopolyyne anions; ab initio quantum chemical methods Acknowledgement: The Austrian Science Fund (FWF) has supported the present research through the Project P27047-N20. This work was also supported by the Ministry of Education, Science and Technological Development of the Republic of Serbia through the Project No. ON- 172040 awarded to S.J. All authors further acknowledge the financial support of the COST Action CM1401, through the short term scientific mission (STSM reference number 39490), awarded to S. J. for a visit to the University of Innsbruck. The computational results presented have been achieved in part using the HPC infrastructure LEO of the University of Innsbruck. References: [1] Etim E. E., Gorai P., Das A., Chakrabarti S. K., Arunan E., 2016, Astrophys. J., 832, 144. [2] Werner H. J., Knowles P. J., Knizia G., Manby F. R., Schtz M. et al., 2012, MOLPRO, version 2012.1, a package of ab initio programs.

12 Hydrogen and nitrogen isotopes follow different fractionation pathways in interstellar clouds

K. Furuyaa

aCenter for Computer Sciences, University of Tsukuba, Japan Contact: [email protected]

Molecular isotope ratios are essential tools to investigate the origin of solar system materials and their possible chemical link with interstellar materials. The most primitive materials in the solar system, such as cometary ices, show the enrichment of both deuterium and 15N compared to the Sun. On the other hand, observations towards low-mass dense cores, where sun-like stars form, have found that molecules in the cold gas are highly enriched in deuterium, but do not show 15 + clear N enrichment. In particular, N2H , which is a daughter molecule of N2 (i.e., possible main budget of gaseous nitrogen), is clearly depleted in 15N in several prestellar cores. It is unclear what the main 15N fractionation mechanism is, and why interstellar molecules in the gas phase tend to be depleted in 15N, while cometary volatiles are enriched in 15N. In this presentation, we present results of gas-ice astrochemical simulations including hydrogen and nitrogen isotopes, which traces the evolution from the formation of molecular clouds to denser cores. We find that nitrogen isotope fractionation mostly occurs in a molecular cloud by the combination of isotope selective photodissociation of N2 and ice formation. In the molecular cloud, where external UV radiation field is not fully shielded, 14N15N is selectively photodisso- 14 15 15 ciated w.r.t N2, which results in the enrichment of N in atomic nitrogen. As N-enriched atomic nitrogen is converted to ammonia ice and HCN ice via grain surface reactions, the bulk gas becomes depleted in 15N, while the icy species are enriched in 15N. Once external UV radia- tion field is sufficiently shielded (i.e., in dense cores), 15N fractionation does not proceed anymore and the molecular 14N/15N ratios established in the molecular cloud stage are largely conserved, because nitrogen isotope exchange reactions are not efficient even at ∼10 K. The 15N-rich ices could be eventually incorporated to protoplanetary disks, in which comets will form, while 15N + is deficient in gases including N2H in dense cores. This situation is very different from deu- terium fractionation; it is mostly driven by hydrogen isotope exchange reactions and becomes more efficient with time as long as temperature is cold. We also discuss how the studies of 15N fractionation constrains nitrogen chemistry in the ISM.

13 Nitrogen isotope fractionation – Can models be reconciled with observations?

E.S. Wirstr¨oma, S.B. Charnleyb

aDepartment of Space, Earth and Environment, Chalmers University of Technology, Sweden; bAstrochemistry Laboratory, Code 691, NASA Goddard SFC, USA Contact: [email protected]

A central issue for understanding the formation and evolution of matter in the early Solar System is the relationship between the chemical composition of star-forming interstellar clouds and that of primitive Solar System materials. The pristine molecular content of comets, interplanetary dust particles and carbonaceous chondrites show significant bulk nitrogen isotopic fractionation relative to the solar value of 14N/15N ∼ 440. Meanwhile their potential precursors, nitrogen- bearing molecules in star-forming molecular clouds, are observed to exhibit a range of isotopic fractionation ratios. Chemical model calculations indicate that atom–molecular ion and ion–molecule reactions in cold dark clouds could account for most of the fractionation patterns observed. However, more recent quantum-chemical computations demonstrate that several of the key processes are unlikely to occur in dense clouds, with the result that models fail to reproduce key 15N enhancements. The talk will present the latest predictions from our nitrogen fractionation model, provide an + overview of fractionation ratios measured in HCN, HNC, CN, NH3, and N2H , and discuss possibilities to reconcile theoretical models with observations.

14 Species-to-species rate coefficients for the + H3 + H2 reacting system

O. Sipil¨aa, J. Harjua,b, P. Casellia

aMax-Planck-Institute for Extraterrestrial Physics (MPE), Giessenbachstr. 1, 85748 Garching, Germany bDepartment of Physics, P.O. Box 64, 00014 University of Helsinki, Finland Contact: [email protected]

+ Deuterium-containing chemical species such as NH2D and N2D are excellent probes of the innermost areas of star-forming cores where density is high and temperature is low. The reason for this is that deuterium substitution occurs efficiently in these conditions, where otherwise abundant neutral species such as CO are frozen onto dust grains. Deuterium is most efficiently + + + + transferred to the various species by the deuterated forms of H3 (H2D ,D2H , and D3 ), + making the treatment of the H3 + H2 reacting system the most important factor in modeling deuterium chemistry in the ISM. Chemical models have so far considered so-called ground-state- to-species rate coefficients for this system, where the effect of rotational excitation on the overall + chemistry is ignored. However, H2D in particular is observed in emission in a wide variety of environments, indicating that rotational excitation is efficient at low temperature, justifying a study of its possible effect on chemical evolution. In this talk I present the results from a + recent paper where we built a new set of rate coefficients for the H3 + H2 reacting system, taking rotational excitation into account, and demonstrate the effect of the new coefficients in pre-stellar andA protostellar&A proofs: manuscript conditions. no. 31039 We find that taking rotational excitation into account makes a clear difference in conditions representing the outer areas of protostellar cores, and that the difference with respect to the models using ground-state-to-species coefficients grows with the degree of deuterium substitution.

+ Figure 1: Abundances+ of the H isotopologs derived using three different6 types3 of rate Fig. 2. Total abundances (sums over spin states) of the various H3 isotopologs as3 functions of time. The medium density is n(H2) = 10 cm (upper 7 3 row) or n(H2) = 10 cm (lower row).coefficients From left to right, at two the panels different show temperatures. calculations assuming Tgas = Tdust = 10 , 15, or 20 K. Species-to-species rate coecients are adopted in two of the models (method 1, dashed lines; method 2, solid lines). The dotted lines show the results of calculations using the ground-state-to-species rate coecients. 15

2.3.1. Local thermal equilibrium accessible owing to our assumptions (see Table 1). However, for + + H3 and D3 , we again assume that all levels can be populated We consider first a scheme where all of the excited rotational regardless of the medium density. states are accessible as long as the medium density is higher Because the values of the rate coecients are now strictly than the critical density of the first excited rotational state of + + tied to the density, the rate coe cients need to be calculated on (o,p)H2D or (o,p)D2H . This situation corresponds to local a case-by-case basis and the construction of a ready-made reac- thermodynamic equilibrium (LTE). One great advantage of this tion set is not practical. Instead, the calculation of the rate coe- approach is that it allows the construction of a reaction set that cients is performed internally in our chemical code. We call this can be easily read into a chemical model. We calculated the restricted-state approach “method 2”. species-to-species rate coecients for all reactions included in + the H3 + H2 reacting system and fitted the results with a modi- fied Arrhenius rate law in the temperature range 5-50 K. The re- 3. Results sulting reaction set is given in Table B.2. We stress that the rate + coecients given in this table are only applicable for (o,p)H2D 3.1. Single-point models + or (o,p)D2H depending on the medium density as explained + + Figure 2 shows the abundances (sums over spin states) of the above. Because H3 and D3 are homonuclear molecules and + H3 isotopologs as calculated with single-point chemical models do not have a permanent dipole moment, we assume that the assuming di↵erent values of medium density and temperature species-to-species rate coecients can be used at all medium (Tgas = Tdust). Figure 3 shows the spin-state abundance ratios in densities for these species. In what follows, we refer to this LTE- the same models. One feature of the models is immediately ev- based approach as “method 1”. ident: the di↵erence between methods 1 and 2 is small, that is, one can employ the species-to-species rate coecients given in 2.3.2. Restricted states Table B.2 with good confidence when modeling cold and dense environments. We checked that at T = 50 K the di↵erence be- + + A more careful treatment of the (o,p)H2D or (o,p)D2H tween methods 1 and 2 remains smaller than a factor of two. + species-to-species rate coecients involves selecting only those However, at such a high temperature the abundances of the H3 states that have a critical density below the medium density. Fur- isotopologs are so low that the chosen method is of no practical ther restrictions apply: For example if the medium density is significance. 7 3 + n(H2) = 5 10 cm , we include only the 101,110, and 212 The total abundances of the H3 isotopologs are una↵ected ⇥ + + rotational levels of pD2H and not the 303 level, even though it by the changes in the H3 + H2 rate coecients at T = 10 K. is allowed by the medium density, because the 221 level is not The di↵erence between the ground-state-to-species model and

Article number, page 4 of 22 Surface astrochemistry: a computational chemistry perspective

H.M. Cuppena, A. Fredona, and M. Simonsa

aInstitute for Molecules and Materials, Radboud University, Nijmegen Contact: [email protected]

Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. Especially, saturated, hydrogen-rich molecules are formed through surface chemistry. I will show how computational chemistry techniques can help answer fundamental questions regarding grain surface chemistry. Two of these questions concern the return of products formed on the grain surface into the gas phase and the role of diffusion in grain surface chemistry. I will show how excess energy of surface reactions can be applied for both processes. To this end, thousands of Molecular Dynamics simulations were performed of one molecule on top of water ice surface, which received a large kinetic energy. Molecules are found to desorb, diffuse, and change the water ice structure. Most molecules only move a few sites, but the distance can be as large as 250 A,˚ which has consequences for follow-up reactions. The desorption probability correlates with the binding energy of the species. For now, the focus has been on simple molecular species, like H2O, CH4, and CO2, but with the aim to make it more general to obtain predictive power for more complex species. I will further show how complex molecules like methanol, formaldehyde, glycoaldehyde, ethylene glycol, and methyl formate can even form at dark cloud conditions. This process is triggered by CO hydrogenation and does not require any external energy source nor the radical species to be mobile. The gas phase CO and H abundance crucially determine which reaction pathway will dominate: towards methanol or towards ethylene glycol. We further see that mobility of grain surface species is crucial in shaping the surface morphology. Rough, fractal-like surfaces appear to block further mantle build-up.

16 On the nucleation of stoichiometric (Al2O3)n clusters

D. Gobrechta, S. T. Bromleyb,c

aInstitute of Astronomy, KU Leuven, Celestijnenlaan 200D, B-3001 Leuven, Belgium bDepartament de Ci`enciade Materials i Qu´ımica F´ısica & Institut de Qu´ımica Te´orica i Computacional (IQTCUB), Universitat de Barcelona, E-08028 Barcelona, Spain cInstituci´oCatalana de Recerca i Estudis Avan¸cats(ICREA), E-08010 Barcelona, Spain Contact: [email protected]

Nano-sized aluminum oxide (alumina) clusters are of increasing interest in Astrochemistry. Quantum effects impact energies, geometries and coordination of these small clusters which cannot be derived from bulk analogues. Hence, the derivation of alumina cluster properties remains challenging. Silicate dust constitutes the major part of oxygen-rich cosmic dust. However, owing to its low thermal stability, the silicate nucleation solely from gas-phase precursors is energetically hampered. Instead, it is more likely that the silicate dust forms on top of pre-existing seed nuclei. These seed nuclei must form from available atoms and molecules, and have to sustain the extreme thermodynamic conditions close to the stellar surface. In oxygen-dominated regimes, the latter requirement are fulfilled by highly refractory metal oxides like alumina (Al2O3). We employ the Monte-Carlo Basin-Hopping (MC-BH) global optimisation technique with inter- atomic pair potentials to generate low-energy candidates of stoichiometric alumina clusters ((Al2O3)n, n=1-10). The candidate structures are subsequently refined with density functional theory calculations employing hybrid functionals (B3LYP and PBE0) and a large basis set (6- 311+G(d,p)) including a vibrational analysis. For the sizes n=8, 9, and 10, we report the discovery of a set of energetically low-lying alumina clusters, including new global minimum candidates, with shapes that are elongated rather than spherical. An illustrative example of the (Al2O3)8 global minimum candidate structure is depicted in Figure 1. We find that the stability limit for these clusters is around a temperature of T'1400 K corresponding to a phase transition in liquid alumina.

Figure 1: Global minima candidate structure of the alumina octomer (Al2O3)8

17 Understanding magnesium silicates with computational chemistry

A. Maci`aEscatllara, C. J¨agerb, S. Bromleya,c aDepartament de Cincia dels Materials i Qumica Fsica & IQTCUB, Universitat de Barcelona, Spain; bLaboratory Astrophysics Group of the Max Planck Institute for Astronomy,Friedrich Schiller University Jena, Germany cInstitut Catalana de Recerca i Estudis Avan¸cats,Spain Contact: [email protected]

Even when astronomical silicates are known to be present everywhere in space, there are several open questions regarding their structure, composition and properties. Computational chemistry can provide new insights into the physical and chemical properties of this family of materials, specially at the nanoscale where no experimental values are available and the properties have to be extrapolated from bulk data. In this talk I’ll discuss our current progress in the areas of nanocluster modelling and amorphous nanoparticle modelling. The population of ultra small silicates (nanoparticles which contains up to few hundreds of atoms) is estimated to be nearby 10% of the total mass of Si. However, since the efficiency of photoelectric heating scales inversely with size, small nanoparticles can have a very strong contribution on both the heating and infrared spectrum of the ISM. The properties of such nanoparticles have a very strong correlation with the structure, which is not feasible to obtain nor study in current experimental setups. We have performed an extensive global optimization search using a new derived inter atomic potential followed by density functional theory calculations in order to obtain reliable structures and energies for the Olivine (Mg2SiO4)N and Pyroxene (MgSiO3)N stoichiometries with N = 1-10. The energy per unit of the nanoclusters allows to determine specially stable structures, which are known to be extremely abundant in laser beam experiments. This very stable particles are referred to ”magic” clusters. We have identified the presence of a Pyroxene magic cluster, which we predict should be possible to detect in astronomical objects. The IR spectra of astronomical silicates are also known to show several shifts. These are ratio- nalized by changes in shape, composition, porosity and other properties, but it is not possible from the experimental point of view to reproduce the variety of IR spectra obtained in circum- stellar shells. Molecular dynamics simulations can be a tool to probe the relationship between shifts in the IR spectra and properties of the nanoparticles. We have developed a series of scripts that allow us to generate models of astronomical silicates of sizes of 5nms, from which several of this properties will be extracted. To support our nanosilicate calculations, preliminary experimentals studies are probing the size dependency and structure of embedded nanosilicate nanocrystallities.

18 Chemistry of exoplanet atmospheres

Ch. Hellinga,b

a Centre for Exoplanet Science, University of St Andrews, St Andrews, UK b School of Physics & Astronomy, University of St Andrews, St Andrews, UK Contact: [email protected]

The ≈ 4000 known extrasolar planets appear in an unprecedented diversity, and non of them resembles any of the solar system planets. Ongoing efforts to study the chemical composition of exoplanet atmospheres by spectroscopic analysis are often hampered by the presence of clouds which hide large parts of the atmosphere from our views. The chemistry and physics of the formation of clouds is therefore an essential part of understanding the chemical regimes any of the planets maybe in. Tidally locked giant gas planets, for example, may have a dayside where the gas is thermally ionised and cloud-free, but the nightside is cool and cloud formation occurs. Such planets resemble stellar atmosphere chemistry on the dayside and planetary chemistry on the nightside. I will discuss the gas-phase chemistry in extrasolar planet atmospheres and show that it is not refined to CO, H2O and/or CH4. Cloud formation starts with the formation of molecular clusters which subsequently grow to macroscopic particles/aerosols that deplete the local gas phase and are a strong opacity source for the atmosphere. I will outline basic concepts for modelling cloud formation processes and discuss exoplanet cloud characteristics like particles sizes, material composition and their feedback onto the atmosphere’s element abundances. I will conclude with ideas on planets as global objects where high-energy particles and radiation affect the local chemistry and the degree of ionisation.

element depletion element enrichment gravitational settling TiO

CO

H2O

nucleation gas phase bulk evaporation bulk material changes by gas-gas reactions due to decreasing gas phase due to changing bulk growth cluster thermal stability thermal stability by gas-surface reactions formation with increasing Tgas

exoplanet change change the cloud in and material mix particles size they are made of warm cold (Tgas < 500K) (Tgas > 2500K)

Figure 1: Cloud formation in exoplanet atmospheres: The nucleation is the most complex process and the bulk growth has the largest impact on the gas phase by element depletion.

19 Comet chemistry: lessons from 67P/Churyumov-Gerasimenko

Kathrin Altwegga, H. Balsigera, J.-J. Berthelierb, J. de Keyserc, S.A. Fuselierd, T.I. Gombosie, M. Rubina

aSpace Research and Planetary Science, University of Bern, Switzerland; bLATMOS/IPSL-CNRS-UPMC-UVSQ, France cRoyal Belgian Institute for Space Aeronomy, BIRA-IASB, Belgium dSpace Science Directorate, Southwest Research Institute, USA eDepartment of Climate and Space Sciences and Engineering, University of Michigan, USA Contact: [email protected]

On 30 September 2016 the European Space Agencys Rosetta spacecraft softly crash-landed on comet 67P/Churyumov-Gerasimenko and brought an intense period of more than 2 years of continuous investigation to an end. Rosetta data led to many discoveries about the origin of the material and the processing in our early Solar System. Among the payload instruments, ROSINA, the mass spectrometer suite, obtained fundamental properties of the comet by analyz- ing the gases emanating from its nucleus. Besides detecting many organic molecules never seen in space before, ROSINA was also able to measure precise isotopic abundances for noble gases as well as D/H in water, NH3 and H2S. Most isotopic ratios turn out to be non-solar, pointing to a heterogeneous nature of the protoplanetary disk. Some of the findings clearly point to unprocessed ice from the prestellar stage which allows to study chemistry in the presolar cloud more or less in situ. Some of the most important findings from ROSINA will be reviewed in the presentation like the zoo of volatile and semi-volatile organics. Although the data analysis from ROSINA is in no way completed similarities to what is found in clouds and star forming regions with the cometary composition are quite striking. The impact of those findings on solar system formation models, on the importance for our Earth and on the question of possible biomarkers will be discussed.

20 C2O and C3O in low-mass star-forming regions

R. G. Ursoa,b,?, M. E. Palumboa, C. Ceccarellic, N. Balucanid, S. Bottinellie,f, C. Codellac,g, F. Fontanig, P. Letoa, C. Trigilioa, C. Vastele,f, R. Bachillerh, G. A. Barattaa, C. Buemia, E. Cauxe, A. Jaber Al-Edharic,i, B. Leflochc, A. L´opez-Sepulcrec,j, G. Umanac, L. Testig,k

aINAF-Osservatorio Astrofisico di Catania, Via Santa Sofia 78, 95123 Catania, Italy; bDip. Scienze Chimiche, Univ. degli Studi di Catania, Viale Andrea Doria 6, 95125 Catania, Italy ?Institut d’Astrophysique Spatiale, Orsay, France; cUniv. Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France; dDip. Chimica, Biologia e Biotecnologie, Univ. degli Studi di Perugia, via Elce di Sotto 8, 06123 Perugia, Italy; eIRAP, Univ. de Toulouse, CNRS, CNES, UPS, Toulouse, France; f CNRS, IRAP, 9 Av. colonel Roche, BP. 44346, 31028 Toulouse Cedex 4, France; gINAF-Osservatorio Astrofisico di Arcetri, L.go E. Fermi 5, l-50125 Firenze, Italy; hObservatorio Astronmico Nacional (IGN), Calle Alfonso XII,3. 28014 Madrid, Spain; iAL-Muthanna Univ., College of Science, Physics Dep., Al-Muthanna, Iraq; jInstitut de Radioastronomie Millim´etrique(IRAM), 300 rue de la Piscine, F-38406 Saint-Martin-d’H´eres, France; kESO, Karl Schwarzchild Str. 2, D-85478 Garching bei M¨unchen,Germany Contact: [email protected]

C2O and C3O, namely dicarbon monoxide and tricarbon monoxide, belong to the carbon chain oxides family. Both molecules have been detected in the gas phase toward various star-forming regions, and the observed abundances have been explained through ion-molecule gas-phase re- actions. Also, laboratory experiments have shown that carbon chain oxides are formed after ion irradiation and UV photolysis of CO-rich icy grain mantle analogues and it has been suggested that these species could be synthesised in the solid phase and then injected in the gas after mantles desorption. With the aim to contribute in the debate about the synthesis of C2O and C3O in space, in this work we report about a multidisciplinary approach in which new detec- tions of both species obtained with Noto-32m and IRAM-30m telescopes have been interpreted through the results of a gas-phase model that allows to simulate the synthesis and destruction of both species and the results of experiments in which carbon chain oxides are produced after ion bombardment (with 200 keV H+) of CO-rich icy grain mantle analogues. Our results strengthen the hypothesis that C2O and C3O are synthesised in the solid phase after energetic processing of icy grain mantles. The subsequent desorption induced by non thermal processes determines their injection in the gas-phase around young sources, where they are detected.

21 Characterization of neutral and charged forms (anions and cations) of the carbon chains C3H and C5H

S. C. Bennedjaia, M. L. Senenta, D. Hammout`eneb

aDepartamento de Qu´ımica y F´ısica Te´oricas, Instituto de Estructura de la Materia, CSIC, Serrano 121, Madrid 28006, Spain; bLaboratory of Thermodynamics and Molecular Modeling, Faculty of Chemistry, USTHB, BP32, El Alia, 16111, Bab Ezzouar, Algiers, Algeria. Contact: [email protected]

Highly correlated ab initio calculations are employed for the structural and spectroscopic char- acterization of small even chains type C2n+1H, considering neutral forms, anions, and cations. The work confirms the stability of the linear carbon chains and carbon clusters containing three- body rings. Whereas, the smallest species C3H displays two stable structures, C5H possesses at least 8 neutral isomers and 10 and 10 isomers with a negative or a positive charge. The lowest energy structures, which can be candidates for laboratory and astrophysical detection, were studied using the RCCSD(T)-F12 and MRCI/CASSCF levels of theory, specifying proper- ties for various electronic states. Neutral C5H displays two prominent equilibrium structures, a 2 hydrogen-terminated linear form (l1-C5H, X Π) and a C2v form containing a three-carbon ring X (l1-C5H, 2 B2) which energy difference was found to be 0.14 eV. For the linear one, Renner-Teller and spin-orbit effects are expected.Its equilibrium spin-orbit constant —Aso,e— was predicted to −1 + be 27.51 cm . The C5H cation presents two prominent forms, one linear and one containing a − − three-carbong ring. Four different stable isomers for the anion, C5H , a linear triplet (l1-C5H , X3Σ−) and three rings. For all of them, rotational constants and dipole moments are provided. Excitation energies to the lowest electronic states were computed. The results are compared with previous experimental data and theoretical calculations searching for propensity rules.

22 Polycyclic Aromatic Aliphatic mixed hydrocarbons in the interstellar medium?

T. Pinoa

aInstitut des Sciences Mol´eculaires d’orsay, CNRS, Universit´eParis Sud, Unversit´e Paris-Saclay, France Contact: [email protected]

All carbon hybridizations are observed in space albeit in different amounts. The aromatic sp2 phase is mainly observed in IR emission via the aromatic infrared bands and through the UV + bump, with a probable contribution to the DIB spectrum as exemplified by the C60 detection. Aliphatic carbon is mainly observed in IR absorption for the sp3 form observed in interstellar grains and through rotational spectroscopy of molecules for the sp form. The link between these components, their possible coexistence, are still questionned. For instances experiments on laboratory analogues of carbonaceous nanograins revealed that defects strongly influence the spectra from the IR to the VUV, althought the amount of sp3 aliphatic carbon is very small compared to that of the aromatic sp2 carbon. Recent experiments revealed the dominant role of carbon chains in soot formation, growth and evolution toward a polyaromatic nanostructura- tion, under specific conditions. These results, together with recent calculations, reveal that the interplay between carbons chains and polycyclic aromatic hydrocarbons remains to be explored. A summary of these recent advances will be shown.

23 The entrapment and scrambling of deuterium on polycyclic aromatic hydrocarbons

Sandra D. Wiersmaab, Alessandra Candianc, Joost M. Bakkerb, Jonathan Martensb, Giel Berdenb, Jos Oomensab,Wybren Jan Buma,aAnnemieke Petrignania aMolecular Photonics, Van ‘t Hoff Insitute for Molecular Sciences, University of Amsterdam, PO Box 94157, 1090 GD, Amsterdam, The Netherlands bFELIX Laboratory, Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 7c, 6525 ED Nijmegen, The Netherlands cLeiden Observatory, Leiden University, P.O. Box 9513, NL-2300 RA Leiden, The Netherlands Contact: [email protected]

The fraction of interstellar deuterium stored in polycyclic aromatic hydrocarbons (PAHs) is still of a highly uncertain value. By studying the photo-induced elimination of H and D from D-containing PAH molecules, we aim to investigate photochemical processes underlying deuter- ation in the interstellar medium (ISM). We use two structural isomers of C14H10, anthracene and phenanthrene, and study different possible isotopomers after deuteronation of protonation. + Infrared multiple photon dissociation (IRMPD) mass spectra show H loss from [D − C14H10] , + while [H − C14D10] shows a strong preference for the loss of D. Transition state calculations revealed facile H/D migration, readily achieved with the available energy. IR spectra of the different isotopomers were recorded and compared with density function theory (DFT) calcu- lations. These show an excellent match with the predicted lowest energy isomer, where the aliphatic deuteronation/protonation site is on the middle ring. All results combined make the case for a scrambling mechanism that takes place after photo-excitation, creating isomers with different aliphatic locations. Considering the astrochemical environment, we speculate that large, compact PAHs with an initial aliphatic C − DH group on solo sites might become respon- sible for the aromatic C − D stretches after photochemical processing, as seen in astronomical spectra.

+ Figure 1: Energy scheme for 1,2-hydrogen shifts on [H − C14D10] phenanthrene, showing the transition states and intermediate state. Energies in eV.

24 Newly discovered interstellar molecules: A challenge for chemical models

M. Ag´undeza, N. Marcelinoa, J. Cernicharoa, E. Roueffb, and M. Tafallac

aInstituto de F´ısica Fundamental, CSIC, Madrid, Spain bLERMA, Observatoire de Paris, France cObservatorio Astron´omico Nacional, Madrid, Spain Contact: [email protected]

The continuous improvement in the sensitivity of radiotelescopes is allowing to unveil the chem- ical composition of molecular clouds with an unprecedented detail. In the current year we have discovered six new interstellar molecules, all them observed in the dense core L483 thanks to a high sensitivity λ 3 mm IRAM 30m line survey. Some of them have been also observed in other dense cores. The discovered species are the cation NS+, which is ubiquitous in different types of interstellar environments (Cernicharo et al. 2018), the radical HCS and its metastable isomer HSC, which provide new observational constraints on the chemistry of sulfur in dark clouds + (Ag´undezet al. 2018a), the radical NCO and the ion H2NCO , which are key precursors in the synthesis of the widespread HNCO and its related isomers (Marcelino et al. 2018), and CNCN, a metastable isomer of the non polar and thus radio invisible molecule cyanogen (NCCN) which is the simplest member of dicyanopolyynes, a family of molecules that is very likely fairly abundant in interstellar clouds (Ag´undezet al. 2018b). All these discoveries have provided a wealth of observational constraints for chemical models and ultimately are allowing to better understand the chemical richness and the chemical processes at work in dense interstellar clouds.

Figure 1: As an example we show the lines of NCO observed toward L483 with the IRAM 30 m telescope (Marcelino et al. 2018).

25 A statistical and machine learning approach to the study of astrochemistry

S. Vitia

aDepartment of Physics and Astronomy, University College London, UK Contact: [email protected]

In order to draw the real potential of molecules as tracers of the dense gas that, among other things, form stars and eventually planets, accurate estimates of the abundances of molecular species as a function of all the parameters that influence their chemistry must be obtained. In other words, we need to understand the chemistry behind each molecule and its dependencies on the density, temperature and energetics of the gas before molecules can be truly powerful tools. Coupling chemical and radiative transfer models for the interpretation of molecular emission has been successful in achieving the above to different degrees, depending on whether one wants to model the physical and chemical structure of the gas, or the microprocesses that lead to complex chemistry in space. However understanding the physical conditions in molecular gas is an inverse problem subject to complicated chemistry that varies non-linearly with both time and the physical environment. Traditionally astrochemistry has always been dominated by trial and error grid-based analysis combined with simple statistics, an approach that may become ineffective when datasets (e.g from ALMA) and/or parameter space are large, complex, or heterogeneous. In this talk I will present a new approach that our group has developed for the interpretation of astrochemical modelling using Bayesian and Machine Learning techniques.

26 Some challenges in modelling the chemistry of planetary disks

W.-F. Thia, S. Hocukb, I. Kampc, P. Woitked,e, Ch. Rabc, S. Cazauxf, P. Casellia, M. D’Angeloc,g

aMax Planck Institute for Extraterrestrial Physics, Giessenbachstrasse, 85741 Garching, Germany bCentERdata, Tilburg University, P.O. Box 90153, 5000 LE, Tilburg, The Netherlands c Kapteyn Astronomical Institute, University of Groningen, Postbus 800, NL-9700 AV Groningen, The Netherlands dSUPA, School of Physics & Astronomy, University of St. Andrews, North Haugh, St. Andrews, KY16 9SS, UK eCentre for Exoplanet Science, University of St Andrews, St Andrews, UK f Faculty of Aerospace Engineering, Delft University of Technology, Delft, The Netherlands gZernike Institute for Advanced Materials, University of Groningen, P.O.Box 221, 9700 AE Groningen, The Netherlands Contact: [email protected]

Modelling the chemistry of protoplanetary disks requires to simulate reactions for large ranges of gas temperature (5 to 10,000 K), of dust temperatures (5 to 1500 K), of density (104 to 1018 cm−3), of radiation fields (UV, X-ray), and of particle fields (cosmic-rays, stellar particles). I will briefly discuss the solutions found by the ProDiMo team to overcome a couple of specific challenges:

• Forming H2 from physisorbed H atoms (Td > 20 K) when dust grains are too warm is not possible. Other paths have to be considered: chemisorption and formation via hydrogenated PAHs.

• At high gas and dust temperature, chemisorption of water on and in dust grains become possible. We implemented the formation of hydrated silicate in the protoplanetary disk physico-chemical code ProDiMo. Water vapor can be quickly trapped in silicate grains before the phase of planet formation. Although hydrated silicates have been found in meteorites and on the surface of asteroids, their formation mechanism is debated. The detection of hydrated silicate in grains around protoplanetary disk would strongly support our proposed formation mechanism.

• Modeling the different charge carriers in disks is paramount to estimate the disk ioniza- tion fraction, which in turn can control the strength of large-scale magnetohydrodynamic turbulence. Magnetohydrodynamic turbulence is key for the disk dynamical evolution. Molecular line profiles are affected by the level of gas turbulence and can be used to test our modeled disk ionization fraction.

27 Sensitivity analysis of kinetic model for chemical reactions in prebiotic atmospheres

D. Truneca, V. Maz´ankov´ab aFaculty of Science, Masaryk University, Brno, Czech Republic; bFaculty of Chemistry, Brno University of Technology, Brno, Czech Republic Contact: [email protected]

A zero-dimensional kinetic model for chenical reactions in prebiotic atmospheres has been de- veloped. This model is focused mainly on chemical reactions in a gaseous mixture of nitrogen (N2), methane (CH4) and carbon dioxide (CO2). Such a mixture simulates the composition of the early Earths prebiotic atmosphere. The reactions and their rate coefficients were taken from Loisson el al. [1], Pintassilgo et al. [2] and Gaens et al. [3].To keep this model as simple as possible it was assumed that N2, CH4 and CO2 are already dissociated by electron impact or by other processes at the start of calculation. After 1 ms of reaction time the model predicts almost constant concentrations of stable products. The products with the highest concentrations are molecular hydrogen (H2), CH4, HCN, CO, molecular oxygen (O2), H2O, cyanogen (C2N2), cyanoacetylene (HC3N) and ethane (C2H6). In comparison with experimental results the model predicted correctly the high concentration of HCN, the CO concentration is slightly lower, which is also in good agreement with experiments. The H2O concentration is predicted to be lower than the CO concentration again in agreement with experiments. However, the NH3 concentration predicted by the model is four orders lower than in the experiments. This supports the hypothesis that NH3 is created by surface processes [4], which are not included in the model. The model also correctly predicted the lower acetylene concentration observed in the experiments. The model predicted production of formaldehyde, however this compound was not detected in the experiments. Two methods of sensitivity analysis have been applied to this kinetic model, which revealed the most important reactions for production of most abundant products.

[1] J.C. Loison, E. Hebrard, M. Dobrijevic, K.M. Hickson, F. Caralp, V. Hue, G. Gronoff, O. Venot, Y. Benilan, Icarus, 247, 218 (2015).

[2] C. D. Pintassilgo, O. Guaitella, A. Rousseau, Plasma Sources Science and Technology, 18, 025005 (2009).

[3] W. Van Gaens, A. Bogaerts, Journal of Physics D: Applied Physics, 47, 079502 (2014).

[4] G. Horvath, N. J. Mason, L. Polachova, M. Zahoran, L. Moravsky, S. Matejcik, Plasma Chemistry and Plasma Processing, 30, 565 (2010).

28 Challenges for astrochemical modelling: uncertainties in chemistry

Jean-Christophe Loisona

aInstitut des Sciences Molculaires - Talence (France) Contact: [email protected]

The study of how molecules form and evolve at low temperatures is the primary objective of as- trochemistry. Significant advances have been made in this field over the last few decades through the application of sophisticated techniques and high-level calculations. However, some critical processes remain poorly known. In my talk, I will review some of these poorly characterized processes and their effects on astrochemical modelling.

29 The CO depletion puzzle in protoplanetary disks

Ewine van Dishoecka aLeiden Observatory, Leiden University, The Netherlands

30 X-rays and other high-energy ionization sources in protoplanetary disks

Ch. Raba, M. G¨udelb, M. Padovanic, I. Kampa, P. Woitked, W.-F. Thie

aKapteyn Astronomical Institute, University of Groningen, The Netherlands; bUniversity of Vienna, Dept. of Astrophysics, Austria; cINAF-Ossevatorio Astrofisico di Arcetri, Firenze, Italy; dSUPA, School of Physics & Astronomy, University of St. Andrews, UK; dMax Planck Institute for Extraterrestrial Physics, Germany Contact: [email protected]

High energy ionization sources such as X-rays, cosmic rays and stellar energetic particles (stellar cosmic rays) can ionize molecular hydrogen, the most abundant chemical species in the envi- ronment of young stars. Therefore, they play a crucial role in the chemistry and evolution of protoplanetary disks. In our model we consider various high-energy disk ionization sources such as stellar X-rays, X- ray background fields (see Figure 1), galactic cosmic rays and stellar energetic particles. With the radiation thermo-chemical disk code ProDiMo (PROtoplanetary DIsk MOdel) we study their impact on the disk chemistry and on spectral line emission for molecules such as HCO+ + and N2H . By means of a representative T Tauri disk model we discuss the impact of the various ionization sources on disk chemistry and possible ways to disentangle their individual contributions to disk ionization via observations. We argue that high spatial resolution observations with modern (sub)mm telescopes provide a way to put observational constraints on the X-ray background flux (see Figure 2) in star- forming regions and the possible strong stellar energetic particle emission of young solar-like stars. However, detailed self-consistent modeling is required as e.g. the dust as the main absorber of UV radiation and UV driven ion-chemistry can have a significant impact on the + + chemical abundances of HCO and N2H .

29 5 LX =10 ; XBGF=10− XBGF 10−4 -13 −5 0.4 1013 XBGF 10 XBGF 10−6 no XBGF ] ]

-15 2 0.3 1 12 − − 10 [s X z/r -13 -15 ζ 0.2 -17 11 log 10 N [cmN

0.1 -17 XBGF dominated -19 10 -19 10 0.0 10-1 100 101 102 100 200 300 400 r [au] r [au]

Figure 1: X-ray ionization rate ζX for a model Figure 2: Impact of X-ray background fields 29 −1 + with LX = 10 erg1 s and a typical X- (XBGF) on the N2H column densities for a ray background field flux of FXBGF = 2 × representative T Tauri disk model. The stellar −5 −2 −1 30 −1 10 erg cm s . The white solid contour line X-ray luminosity is LX = 10 erg s and the −19 −1 encloses the region where the XBGF dominates cosmic-ray ionization rate is ζCR ≈ 10 s over the stellar X-ray emission.

31 FTIR analysis of the products of a negative corona discharge in a N2-CH4 mixture with added CO2

V. Mazankovaa,e, L. Torokovaa, L. Moravskyb, S. Matejcikb, D. Trunecc, Z. Navratilc, N. J. Masond

aFaculty of Chemistry, Brno University of Technology, Brno, Czech Republic; bDepartment of Experimental Physics, Comenius University, Bratislava, Slovakia; cDepartment of Physical Electronics, Masaryk University, Brno, Czech Republic; dSchool of Physical Sciences,The Open University, Milton Keynes, United Kingdom; eUniversity of Defence, Brno, Czech Republic Contact: [email protected]

A negative corona discharge operating at atmospheric pressure has been used to initiate chem- ical reactions in a gaseous mixture of nitrogen, methane and carbon dioxide. Such a mixture simulates the composition of the early Earths atmosphere. This work extends our previous experimental studies of the chemistry of prebiotic atmospheres generated in an atmospheric pressure glow discharge. The present work is devoted to the study of the role of CO2 in pre- biotic atmospheric chemistry. The gas mixture was composed of nitrogen with 2-4 % methane and 1 % CO2. The corona discharge was characterised by electrical measurements and optical emission spectroscopy. The reaction products from discharge were further analyzed by FTIR spectroscopy. The composition of solid products deposited on the electrode tip was obtained by EDX analysis. The specific input energy was altered during the experiments and the con- centration of all products was found to increase with its increase. It was further shown that while the addition of CO2 admixture leads to the generation of CO and H2O, no other com- pounds containing oxygen were detected. The energy yields of products were calculated and good agreement with energy yields obtained in previous experiments was found.

32 Controlled ion-molecule reactions

A. Lopesa, C. Romanzina,b, R. Thissena, C. Alcaraza,b

aLaboratoire de Chimie Physique, UMR 8000 CNRS – Universit´eParis-Sud et Paris Saclay, Orsay, France; bSynchrotron SOLEIL, L’Orme des Merisiers, St Aubin, France Contact: [email protected]

We will present experimental studies of ion-molecule reactions in the gas phase in which the various forms of energy before the reaction are controlled and their effects characterized. For cations and anions, the collision energy is varied from thermal values to few eV. For cations, further control is made on their internal excitation (electronic or vibrational) through coincidence techniques and the use of VUV photoionisation at the SOLEIL synchrotron [1,2]. The motivations are not only the understanding of the reaction dynamics, but also the determi- nation of absolute reaction cross sections or rate constants useful for the modelisation of complex media such as planetary ionospheres, the interstellar medium and cold plasmas. The experimental apparatus, CERISES, is available for external users through an association of the LCP team with the SOLEIL synchrotron, thereby extending the offer of advanced studies in chemistry by this facility. This has allowed groups from Prague (M. Polasek, J. Zabka et al), Trento (D. Ascenzi et al) and Stockholm (W. Geppert et al), participating to the COST CM1401 “Our Astro-Chemical History”, to conduct experimental studies on excited ion reactivity [2–4]. Recent developments of the CERISES apparatus allow for the preparation of new kinds of parent + + ions such as R and (M)n by photoionisation of neutral radicals (R) or clusters (M)n produced in situ in a molecular beam. This opens for important new studies on the compared reactivity of different isomers and on the effect of solvatation on the ion reactivity. +∗ Some examples on the reactivity of vibrationally or electronically methyl cations CH3 with small saturated and unsaturated hydrocarbons [5] will illustrate the advances in the chemistry of excited ions. We acknowledge support from SOLEIL, the LABEX PALM (ERACOP project), the RTRA “Triangle de la Physique” (RADICAUX, GIN and NOSTADYNE projects), the PNP french planetology program and COST Actions CM1401, TD1308 and CM1204.

[1] B.K. Cunha de Miranda et al, J. Phys. Chem. A 2015, 119 (23), 6082–6098 [2] A. Cernuto et al, J. Chem. Phys. 2017, 147 (15), 154302 [3] C.F. Lind´en et al, J. Phys. Chem. A 120(27), 5337–5347 (2016) [4] M. Polasek et al, J. Phys. Chem. A 120(27), 5041–5052 (2016) [5] A. Lopes, PhD Thesis, Universit´eParis-Saclay (Orsay), 2017

33 Frequency-dependent IR-induced restructuring of amorphous solid water

J. A. Noblea, H. M. Cuppenb, S. Coussanc, B. Redlichb, S. Ioppolod aLaboratoire de Physique des Lasers Atomes et Mol´ecules,Universit´ede Lille/CNRS, France; bInstitute for Molecules and Materials, Radboud University Nijmegen, The Netherlands; cLaboratoire Physique des Interactions Ioniques et Mol´eculaires, Aix-Marseille Universit´e/CNRS,France; dSchool of Electronic Engineering and Computer Science, Queen Mary University of London, United Kingdom Contact: [email protected]

Water ice is key to the reactivity occurring on dust grains in star forming regions. The structure of the ice will determine rates of important processes such as adsorption, desorption and diffusion of small molecules, and this structure can be modified by energetic processes, evolving from ASW to crystalline ice as we move from cloud to core to disk. One such process which is little studied is the interation of water ice with infrared photons. Here we present new results on the modification of the ASW structure upon selective IR irradiation. In previous studies we have concentrated on the behaviour of ASW upon selective IR irradiation of its surface dangling modes. When irradiated, the surface molecules reorganise, predominantly forming a monomer-like mode adsorbed to the ice surface. All dangling modes share one common channel of vibrational relaxation; the ice remains amorphous but with a reduced range of binding sites, and thus an altered catalytic capacity. Building on our team’s experience in MIR and THz spectroscopy of ices and molecular dynamics simulations of energetic processes in ices, and taking advantage of the wide tunability of the FE- LIX IR laser at the Institute for Molecules and Materials in Radboud, we irradiate ASW samples at all of its vibrational modes in the mid IR (stretching, bending, libration, and combination) as well as its THz modes. We show that the amorphous ice structure reorganises upon irradiation, becoming more crystalline in nature. This interpretation is confirmed by comparison with MD simulations of energy injection into the individual vibrational modes of ASW. Noble, J. A., Martin, C., Fraser, H. J., Roubin, P. & Coussan, S., “Unveiling the surface structure of amorphous solid water via selective infrared irradiation of OH stretching modes” J. Phys. Chem. Lett. 2014, 5, 826 Allodi, M. A., Ioppolo, S., Kelley, M. J., McGuire, B. A. & Blake, G. A., “The structure and dynamics of carbon dioxide and water containing ices investigated via THz and mid-IR spectroscopy” PCCP 2014, 16, 3442 Coussan, S., Roubin, P. & Noble, J. A., “Inhomogeneity of the amorphous solid water dangling bonds” PCCP 2015, 17, 9429 Fredon, A. Lamberts, T. & Cuppen, H. M., “Energy dissipation and nonthermal diffusion on interstellar ice grains” ApJ 2017, 849, 125

34 VUV spectroscopy of solid benzene and benzene-water system

A. Dawesa, N. Pascualb, Sabrina G¨artnerc, Nigel J. Masona, Søren V. Hoffmannd and Nykola C. Jonesd

aSchool of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom; bDepartment of Chemistry and Physics, La Trobe Institute for Molecular Science, La Trobe University, Melbourne 3086, Australia; cISIS Neutron and Muon Source, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Didcot, OX11 0QX, United Kingdom; dISA, Centre for Storage Ring Facilities, Department of Physics and Astronomy, Aarhus University, Ny Munkegade 120, DK-8000 Aarhus C, Denmark Contact: [email protected]

Most of what we know about the properties of solids in space comes from laboratory interpreta- tion of observations via investigation of condensed phase molecular analogues under controlled laboratory conditions. Much of the focus on the investigation of the optical and spectral prop- erties of these solids has been in mid-infrared spectroscopy, a powerful tool for probing the intermolecular interactions via their influences on the intramolecular vibrational modes. Com- plementary to mid-IR spectroscopy, we have also been exploiting vacuum ultraviolet (VUV) spectroscopy to probe the electronic states of molecular solids since we have previously shown that the electronic states of molecules are also very much influenced by intermolecular interac- tions in the condensed phase [Mason, Dawes et al. Faraday Discussions 133, 311-329, 2006]. The electronic states are affected by deposition conditions, annealing history, sample thickness and temperature as well as sample composition and concentration, requiring detailed systematic lab- oratory studies. Such systematic empirical data is vital for modelling photochemical processes in molecular solids under astrophysical conditions especially as their optical spectra differ greatly from that of the gas phase with shifts in transition energies and changes in photoabsorption cross sections. I will primarily discuss the results of our recent work on the VUV spectroscopy of solid benzene and benzene-water mixtures and layers, carried out at the ASTRID2 synchrotron fa- cility in Aarhus, Denmark, in the context of the influence of large aromatic molecules such as polycyclic aromatic hydrocarbons (PAHs) in interstellar ices. These large molecules have signif- icantly high electronic photoabsorption cross sections in the VUV, orders of magnitude grater than the vibrational absorption cross sections in the mid-IR, allowing for detailed systematic investigation of thin solid films and dilute concentrations within ice mixtures.

35 Densities, infrared band strengths and optical constants of solid methanol.

R. Lunaa, G. Molpeceresb, J. Ortigosob, M. A. Satorrea, M. Domingoa, and B. Mat´eb

aCentro De Tecnolog´ıasF´ısicas, Universitat Polit`ecnica de Val`encia,Plaza Ferr´andiz-Carbonell, 03801, Alcoy, Spain bInstituto de Estructura de la Materia, CSIC, Serrano 121, 28006 Madrid, Spain Contact: [email protected]

The increasing capabilities of space missions, like the James Webb Space Telescope, or ground- based observatories, like the European Extremely Large Telescope, demand high quality labora- tory data of species in astrophysical conditions for the interpretation of their findings. We have measured new physical and spectroscopic data of solid methanol that will help to identify this species in astronomical environments. Methanol ices were grown by vapor deposition in high vacuum chambers. On one hand, ice densities were measured via a cryogenic Quartz Crystal Microbalance and laser interferometry. On the other hand, absorbance infrared spectra of ice layers of different thickness where recorded to obtain optical constants using an iterative mini- mization procedure. Finally, infrared band strengths were determined from infrared spectra and ice densities. Some discrepancies are found between our optical constants and those previously reported in the literature, for an ice grown at 10 K and subsequently warmed. The disagree- ment is explained as due to different ice morphologies. The new infrared band strengths agree with previous literature data when the correct densities are considered [Hudgins et al. 1993, ApJS, 86, 713; Bouilloud et al. 2015, MNRAS, 451, 2145; Luna et al. A&A, DOI:10.1051/0004- 6361/201833463]

4 . 5 x 8 0 x 1 0 4 . 0 1 3 0 K 3 . 5 1 2 0 K

t 3 . 0 e s f f

o 1 1 0 K

+ 2 . 5

e

c 1 0 0 K n

a 2 . 0 b r

o 8 0 K s b

a 1 . 5 6 0 K 1 . 0 4 0 K 0 . 5 2 0 K 0 . 0 4 5 0 0 4 0 0 0 3 5 0 0 3 0 0 0 2 5 0 0 2 2 5 0 2 0 5 0 1 5 0 0 1 0 0 0 - 1 w a v e n u m b e r c m

Figure 1: Infrared spectra of methanol ices layers of 990 nm grown at the indicated temperatures. Spectral regions with weak absorptions have been multiplied by a factor indicated in the figure.

36 Experimental gas-phase reaction kinetics studies for astrochemistry: current status and future directions

Ian R. Simsa aInstitut de Physique de Rennes, UMR CNRS-UR1 6251, Universit´ede Rennes 1, 263 Avenue du G´en´eral Leclerc, 35042 Rennes Cedex, France.

The use of the CRESU (Cin´etiquede R´eactionen Ecoulement Supersonique Uniforme, or Reac- tion Kinetics in Uniform Supersonic Flow) technique (Sims et al. 1994) has enabled us to show that many neutral-neutral reactions may be rapid down to the temperatures of dense interstellar clouds (10 − 20 K), as well as proving an exacting test for theory (Sabbah et al. 2007). Rate co- 1 efficients have been measured as low as 6 K for the reaction S( D) + H2 (Berteloite et al. 2010) and 11 K for the prototypical reaction F + H2 → HF + H (Tizniti et al. 2014). A series of fast barrierless reactions related to the formation of long chain cyanopolyyne molecules H(C2)nCN (Cheikh Sid Ely et al. 2013) of interest in both interstellar clouds and Titans atmosphere, have been studied both experimentally and theoretically, and the latest results involving reactions of CN, C2H and C3N radicals to yield HC5N will be presented. One of the current princi- pal challenges in chemical kinetics is the determination of absolute product-channel specific rate constants for elementary reactions. This is especially true at low temperatures, and I will survey current efforts in Rennes and in collaboration with leading groups elsewhere to use two promis- ing new techniques to determine product branching ratios at low temperatures in combination with the CRESU technique, namely Synchrotron Photoionisation Mass Spectrometry (SPIMS) (Bouwman et al. 2013; Lockyear et al. 2015) and Chirped Pulse microwave spectroscopy in Uniform supersonic Flow (CPUF) (Abeysekera et al. 2015).

References Abeysekera, C., Joalland, B., Ariyasingha, N., Zack, L. N., Sims, I. R., Field, R. W. & Suits, A. G. 2015, J. Phys. Chem. Lett. 6, 1599. Berteloite, C., Lara, M., Bergeat, A., Le Picard, S. D., Dayou, F., Hickson, K. M., Canosa, A., Naulin, C., et al. 2010, Phys. Rev. Lett. 105, 203201. Bouwman, J., Fournier, M., Sims, I. R., Leone, S. R. & Wilson, K. R. 2013, J. Phys. Chem. A 117, 5093. Cheikh Sid Ely, S., Morales, S. B., Guillemin, J. C., Klippenstein, S. J. & Sims, I. R. 2013, J. Phys. Chem. A 117, 12155. Lockyear, J. F., Fournier, M., Sims, I. R., Guillemin, J.-C., Taatjes, C. A., Osborn, D. L. & Leone, S. R. 2015, Int. J. Mass Spectrom. 378, 232. Sabbah, H., Biennier, L., Sims, I. R., Georgievskii, Y., Klippenstein, S. J. & Smith, I. W. M. 2007, Science 317, 102. Sims, I. R., Queffelec, J. L., Defrance, A., Rebrion-Rowe, C., Travers, D., Bocherel, P., Rowe, B. R. & Smith, I. W. M. 1994, J. Chem. Phys. 100, 4229. Tizniti, M., Le Picard, S. D., Lique, F., Berteloite, C., Canosa, A., Alexander, M. H. & Sims, I. R. 2014, Nature Chemistry 6, 141.

37 Molecules at high redshift: from ALMA to the SKA

Jeff Wagga

aSKA Organisation, Lower Withington Macclesfield, Cheshire SK11 9DL, United Kingdom; Contact: [email protected]

The past two decades have seen explosive growth in our ability to study gas in the distant Universe. Beginning with the early observations of cool gas and dust in some of the most extreme high redshift galaxies, we are now regularly detecting faint atomic lines and thermal dust emission in less luminous galaxies well into the Epoch of Reionization, during the first billion years of the Universe. This revolution has been enabled by new submm-to-cm wavelength telescopes like the Atacama Large Millimetre/Submillimetre Array in Chile. The next generation of long wavelength telescopes such as MeerKAT in South Africa are beginning to operate, and should reopen the study of the cold, low-J transitions of faint molecular lines like CO, HCN and CS at high-redshifts. These studies will be further enhanced by SKA1 when it comes online in the next decade, and I will provide an update on the SKA1 design work as it nears completion.

38 The future of surface chemistry

S. Cazauxa, F. Dulieub, G. Munoz Caroc, H. Linnartzd, M. Minissalee

aFaculty of Aerospace Engineering, Delft University of Technology, Kluyverweg 1, 2629 HS, Delft, The Netherlands bILERMA, Universite de Cergy Pontoise et Observatoire de Paris, UMR 8112 du CNRS. 5, mail Gay Lussac, 95031 Cergy Pontoise cCentro de Astrobiologa, INTA-CSIC, Carretera de Ajalvir, km. 4, Torrejn de Ardoz, 28850 Madrid, Spain dLaboratory for Astrophysics, Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden eAix Marseille Universite, CNRS, PIIM UMR 7345, 13397 Marseille, France Contact: [email protected]

Interstellar dust grains have been recognised to be important catalysts for the formation of the simplest (H2) to the most complex molecules (amino acids) in space. While many processes occurring on dust surfaces have been studied experimentally and theoretically during the last decades, the step from experimental and theoretical studies to astrophysical modelling and observations still represents a great challenge. In this talk I will review what we think are the most important processes driving the chemistry on surfaces and our current understanding on such processes. More precisely, I will concentrate on the processes responsible for the reactivity on surfaces (see figure 1) such as diffusion and reaction, as well as what transforms gas phase species to solid species (accretion) and solid species to gas phase species (sublimation and reactive/chemical desorption). The different experiments or theoretical computations used to constrain these processes will be presented. I will discuss some of the critical points from the past studies that still need to be explained, as well as the studies that are envisaged to better understand chemistry on grain surfaces.

Figure 1: Sketch showing different processes governing reactions on surfaces: accretion, diffusion, reaction and chemical desorption.

39 Posters Deuterium Chemistry in Interstellar and Circumstellar environments: A step towards a full spin chemistry

S. Antonellinia, T. J. Millara, C. Walshb aAstrophysics Research Centre, School of Mathematics and Physics, Queens University Belfast, Belfast BT7 1NN, UK bSchool of Physics and Astronomy, University of Leeds, Leeds, LS2 9JT, UK Contact: [email protected]

To date, around 200 molecules have been detected in the Interstellar (ISM) and Circumstellar mediums (CSM). As Hydrogen (H) has two stable isotopes, isotopologues of these molecules have been also observed. The low mass of these atoms, bring to high rotational energies in low mass molecules, and the nuclear spin statistics of H and Deuterium (D), allows only certain rotational states in small molecules with multiple H and or D atoms. The results is that only molecules with certain spin state will be able to react in the coldest and embedded regions of ISM/CSM. Complex chemical networks treated deuteration including species up to 7 atoms, while networks including spin chemistry are limited to a small number of molecules and have been produced only for dark cloud conditions. In this study, we aim to expand chemical network including deuteration for molecules up to 10 atoms and create a consistent treatment of the spin chemistry for the relevant reactions, in the whole conditions of temperature, density, radiation field encountered in the ISM and in Protoplanetary Disks.

104 Non Physical AV < 1 conditions 1800 10-4

-12 1600 10

-20

] 10 1400 0

G -28 [ 10

d l -36 1200

e 10 i T f

g a

-44 s n

10 1000 [ o K i t -52 Non ] a

i 10

d Physical 800

a -60 conditions r 10

V -68 600 U 10 F 10-76 Density beyond 400 10-84 ISM/CSM 200 10-92

10-100 108 109 1010 1011 1012 1013 1014 1015 1016 3 Density [cm− ]

Figure 1: Physical conditions of the Interstellar and Circumstellar environments. Red crosses are our randomly sampled selected models.

41 The OH + CH3OH → CH3O + H2O at low temperatures: a barrierless process

J. Brand˜aoa, J. Moreiraa, G. Lendvayb

aDepartment of Chemistry and Pharmacology, University of the Algarve, Portugal; bInstitute of Chemistry, Hungarian Academy of Sciences, Hungary Contact: [email protected]

The removal of a hydrogen atom from a methanol molecule by the hydroxyl radical producing water and hydroxymethyl or methoxy radicals has been suggested[1] to be a possible source for the presence of methoxy radicals detected in interstellar space[2]. The experimental results display a peculiar behaviour: at temperatures above 200 K the formation of hydroxymethyl radical, CH2OH, dominates with a thermal rate constant that increases with temperature; how- ever at temperatures below 200 K the product CH3O dominates, but the thermal rate constant decreases with temperature, halving its value when temperature increases from 50 K to 200 K. Theoretical calculations[3] on this system have shown that the production of CH2OH involves −1 an energy barrier of 0.5 kcal mol , while the direct production of the methoxy radical, CH3O, involves a barrier of 2.54 kcal mol−1. To explain the low temperature behaviour, Siebrand et al.[3] studied the role of the presence of the methanol dimer on this process. This careful work, extensively debated in the WG1 and WG2 meeting held at Ciudad Real last December, states that under the low temperatures of the supersonic Laval nozzle beam, there coexist a mixture of methanol monomers and dimers, which have a binding energy of 6.1 kcal mol−1. The collision of the hydroxyl radical with the dimer would dissociate it forming a stable CH3OH ··· OH complex. This stable complex would react, by tunnelling, producing the methoxy radical. Here we present an alternative explanation to the experimental findings, keeping the idea of the importance of the presence of the dimer at low temperatures, which they showed to dominate at T < 100 K, being negligible at T > 150 K. We have carried out DFT calculations using B3LYP and MO8-SO functionals for the direct removal of the hydrogen atom from the dimer by the hydroxyl radical and found that this process occurs without barrier. Thus, the reaction rate will be dominated by the capture process known to have a negative temperature dependence. The hydroxyl radical will form a complex with the dimer (energy −16.5 or −17.2 kcal mol−1), and then it will remove the hydrogen atom through an exchange barrier located at −11.0 or −6.6 kcal mol−1 relative to reactants. The resulting water molecule can form another complex with the methanol and the methoxy radical (−25.7 or −25.0 kcal mol−1) or dissociate. Capture calculations are under way to estimate the rate constant.

References

[1] R.J. Shannon, M.A. Blitz, A. Goddard and D.E. Heard, Nat. Chem., 2013, 5, 745-749.

[2] k. Acharyya, R.L. Herbst, e. anf Caravan, R.J. Shannon, M.A. Blitz and D.E. Heard, Mol. Phys., 2015, 113, 2243-2254.

[3] W. Siebrand, Z. Smedarchina, E. Martinez-N´u˜nezand A. Fern´andez-Ramos, Phys. Chem. Chem. Phys., 2016, 18, 22712-22718.

42 Thermal desorption of NH2CHO and CH3NH2 from HOPG and ASW ice surfaces

H. Chaabounia, S. Dianaa, T. Nguyena, F. Dulieua

aLERMA, University of Cergy-Pontoise Paris Seine, 5 mail Gay Lussac, 95000, Cergy, France. CNRS-UMR8112, Observatoire de Paris, France. Contact: [email protected]

Formamide (NH2CHO) and methylamine (CH3NH2) are complex organic molecules of great relevance in prebiotic chemistry. They are the most abundantly amine-containing molecules observed in many astrophysical environments prestellar and protostellar objects, hot corinos, massive hot cores and comets) [1-3]. The presence of these molecules in the gas phase may result from thermal desorption of interstellar ices. We present the experimental and the simulating results for the temperature programmed desorption (TPD) of formamide and methylamine from analogues of interstellar dust grain surfaces (graphite HOPG and np-ASW ice). The aim of this work is to understand the interaction of these amino molecules with the water ice and compare their desorption energies [4]. Thermal desorption experiments of formamide and methylamine ices were performed with the FORMOLISM setup located at LERMA-Cergy laboratory, at temperatures 40-240 K, and in the sub-monolayer and monolayer regimes. The desorption energy distributions of these two molecules were derived from TPD data using a set of independent Polanyi-Wigner equations. Results showed that the desorption of formamide from graphite and ASW ice surfaces occurs at 160-200 K after the sublimation of the water ice at 150 K, whereas the desorption profile of methylamine depends strongly on the substrate. This latter desorbs before and during the desorption of H2O, and even later at T>160 K. In addition, solid NH2CHO fully diffuses through the ASW ice surface towards the graphitic substrate and releases into the gas phase with a desorption energy distribution of 5056-6990 K. Whereras, the large desorption energy distribution of CH3NH2 from the water ice surface is 3900-8420 K, calculated with the pre-exponential factor A=1012 s−1. A fraction (0.15 ML) of solid methylamine diffuses within the water ice and desorbs from the HOPG with higher binding energies (5050-8420 K) that exceed that of the crystalline water ice (4930 K). Implications of these high binding energies are discussed. References: [1] Kahane. C, et al., ApJ, 763, L38 (2013); [2] Lopez-Sepulcre. A, et al., MNRAS, 449, 2438 (2015); [3] Altwegg. K, et al, Sci. Adv., 2, 1 (2016); [4] Chaabouni. H, Diana. S, Dulieu. F., A&A, 612, A47 (2018).

Figure 1: Diffusion and desorption of formamide.

43 The Chemical Evolution from Prestellar to Protostellar Cores: A New Multiphase Model With Bulk Diffusion and Photon Penetration

Qiang Changa, Yang Lua, Yuri Aikawab

aXinjiang Astronomical Observatory, Chinese Academy of Sciences, China; bDepartment of Astronomy, Graduate School of Science, The University of Tokyo, Japan Contact: [email protected]

We investigate the chemical evolution of a collapsing core that starts from a hydrostatic core and finally form a low-mass protostar. New multiphase gas-grain models that include bulk dif- fusion and photon penetration are simulated by the macroscopic Monte Carlo method in order to derive the chemical evolution. Two-phase models and basic multiphase models without bulk diffusion and photon penetration are also simulated for comparison. Our physical model for the collapsing core is base on a one-dimensional radiation hydrodynamics model. We find that abundant radicals, which are precursors of complex organic molecules (COMs), are produced in- side ice mantles in the cold stage of the core in the new multiphase models. Radicals can diffuse inside ice mantles to form COMs when the temperature of the core increases. Photodissociation rates of COMs are reduced by the exponential decay of UV flux within the ice mantle. Thus, COMs produced at a primoridial stage at 10 K in the new multiphase models are about one order of magnitude higher than those in the two-phase model while COMs produced by radical recombination at higher temperatures in the new multiphase models are more than one order of magnitude higher than those in the two-phase and basic multiphase models. Volatile species such as CO and N2 ice sublime from the grain mantle via two processes in the new multiphase models. A small fraction if them sublimes at their own sublimation temperatures while the majority is locked in water ice and deorbs when water ice sublimes. Our model shows a rea- sonable agreement with observations toward low-mass protostars. Moreover, molecular oxygen abundances predicted by our multiphase models agree reasonably with that found in cometary materials.

44 Dynamics for the H2CO + OH reaction

Pablo del Mazoa, Octavio Roncerob, Alfredo Aguadoa

aDepartment of Applied Chemical Physics, Autonomous University of Madrid, Spain; bInstitute of Fundamental Physics, CSIC, Spain Contact: [email protected]

H2CO was the first complex organic molecule (COM) found in the interestellar medium (ISM) [1] and is one of the most abundant there found [2]. Hence, it is of paramount importance to understand its chemistry in the conditions found in the ISM.

A dynamical study of the H2CO + OH → HCO + H2O is presented. This reaction is very interesting at temperatures under 300 K, when the kinetical reaction rate constants increases, showing a clear non-Arrhenius behaviour. To understand this reaction, a full dimensional potential energy surface (PES) for this reaction has been obtained [3] and used in a quassiclassical trajectory study (QCT) as well as preliminary Ring Polymer Molecular Dynamics (RPMD). The results for the QCT study are compared with the experimental ones [4], showing that this PES describes semiquantitatively the behaviour of the kinetical rate constants with respect to temperature, although some discrepancies are found. At low temperatures, quantum effects are expected to play a major role, what would increase the kinetical rate constant. Also some of the discrepancies are intrinsic to the PES and cannot be addresed to quantum effects. That is why more effort is needed in building a new PES for this system.

References

[1] L. E. Snyder, D. Buhl, B. Zuckerman, and P. Palmer, “Microwave detection of interstellar formaldehyde,” Physical Review Letters, vol. 22, no. 13, pp. 679–681, 1969.

[2] A. Bacmann and A. Faure, “The origin of gas-phase HCO and CH3O radicals in prestellar cores,” Astronomy & Astrophysics, vol. A130, p. 587, 2016.

[3] A. Zanchet, P. del Mazo, A. Aguado, O. Roncero, E. Jim´enez,A. Canosa, M. Ag´undez,and J. Cernicharo, “Full dimensional potential energy surface and low temperature dynamics of the H2CO + OH → HCO + H2O reaction,” Physical Chemistry Chemical Physics, vol. 20, no. 8, pp. 5415–5426, 2018.

[4] A. J. Oca˜na,E. Jim´enez,B. Ballesteros, A. Canosa, M. Anti˜nolo,J. Albaladejo, M. Ag´undez, J. Cernicharo, A. Zanchet, P. del Mazo, O. Roncero, and A. Aguado, “Is the Gas-phase OH+H2CO Reaction a Source of HCO in Interstellar Cold Dark Clouds? A Kinetic, Dy- namic, and Modeling Study,” The Astrophysical Journal, vol. 850, no. 1, p. 28, 2017.

45 Accuracy of spectroscopic constants predicted by explicitly correlated coupled cluster methods.

M. Gronowskia

aInstitute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warsaw, Poland aInstitute of Theoretical Physics, Faculty of Physics University of Warsaw, Pasteura 5, 02-093 Warsaw, Poland Contact: [email protected]

Theoretical predictions of spectroscopic parameters by high-level quantum-chemical calculations play an important role in guiding spectroscopic and astronomical studies of complex organic molecules. The reliable prediction of rotational constants requires: i high-level treatment of correlation of valence electrons, ii inclusion of correlation of core electrons, iii inclusion of a vibrational correction. Usually, in order to get high precision, the basis set limit must be reached. This is easily doable for small molecules, but for larger systems this is still challenging. Explicitly correlated (F12) methods offer a significant improvement in basis set convergence compared to the classical version of coupled cluster methods. In consequence, their application to estimation of spectroscopic constants is an appealing approach to larger molecules. We have tested different variants of the explicitly correlated coupled-cluster method using the correlation consistent basis set designed for F12 computations. We compared these values to experimental data. Accuracy of rotational constants on the order of 0.1-0.2% can be reached by using the core valence triple zeta basis set and any variant of explicitly correlated coupled cluster single-double and perturbative triple (CCSD(T)-F12). Further improvements can be obtained by applying a larger basis set or proper selection of the F12 method. Statistical analysis was based on the results obtained for 22 closed-shell molecules (27 rotational constants and 72 fundamental frequencies), including both saturated and unsaturated molecules. For unsaturated hydrocarbons (like acetylene, C2H4), correlation of core electrons is far more important than for saturated hydrocarbons (like ethane, C2H6). This is true for both rotational constants and vibrational frequencies.

46 Planet forming disks: Challenging astrochemical laboratories

I. Kampa, W.-F. Thic, M. D’Angeloa,b, S. Cazauxd, S. Hocuke, P. Casellic, Ch. Raba, P. Woitkef aKapteyn Astronomical Institute, University of Groningen, The Netherlands; bZernike Institute for Advanced Materials, University of Groningen, The Netherlands; cMax Planck Institute for Extraterrestrial Physics, Garching, Germany; dFaculty of Aerospace Engineering, Delft University of Technology, The Netherlands; eCentERdata, Tilburg University, The Natherlands; f SUPA, School of Physics & Astronomy, University of St. Andrews, UK Contact: [email protected]

From observational data collected in the past decades we know that: (1) every young star is born with a disk, (2) disks contain gas and small dust, (3) nearly every star in our galaxy hosts planets. The planets are forming from the material in these disks. Hence, the study of the disk chemical composition is a key factor for understanding how and where planets form and which type of planets are forming (gas giants, super Earth, etc.). We revisited the chemistry on the warm surfaces of small (sub-µm-mm size) silicate grains in a high pressure environment as it likely existed where the Earth was forming. Using Monte Carlo simulations and chemical kinetic models, we demonstrate that: (1) Water can effciently stick to the forsterite surfaces at temperatures of 300-500 K and (2) phyllosilicates can form within 100 000 yr (short compared to the lifetime of the disk) and the amount is limited by the maximum water uptake of the silicate. This result has strong implications for the origin of water on Earth since we find that planetesimals inside the water snowline (building blocks of rocky planets) may contain abundant water. This work demonstrates that complex thermo-chemical models of astrophysical objects can serve as virtual laboratories to study new chemical pathways. They provide a powerful link between laboratory/theoretical work and astrophysical observations.

−2 Figure 1: Left: Surface coverage (H2O nm ) as a function of temperature (K) from Monte Carlo simulations. Right: Steady-state abundance from chemical kinetic models for phyllosilicates inside the dust grains in a young planet forming disk; the white dashed lines indicate temperature contours and the thick dashed line shows the snowline beyond which water exists as ice on the dust grain surfaces.

47 Photochemistry of PAHs embedded in water ice: new insights into the role of ice structure on the reactivity and ionisation energies of PAHs

J. A. Noblea,b, E. Michoulierb,c, N. Ben Amorc, M. Rapaciolic, C. Aupetita, A. Simonc, C. Toubinb, J. Mascettia

aInstitut des Sciences Mol´eculaires, Universit´ede Bordeaux/CNRS, France; bLaboratoire de Physique des Lasers Atomes et Mol´ecules,Universit´ede Lille/CNRS, France; cLaboratoire de Chimie et Physique Quantiques, Universit´ede Toulouse/CNRS, France Contact: [email protected]

Polycyclic Aromatic Hydrocarbons (PAHs) are a family of molecules which represent the best candidates to explain the observation of the Aromatic Interstellar Bands (AIBs), emission fea- tures in the infrared. They could also contribute to some UV-visible absorption features: the so-called Diffuse Interstellar Bands (DIBs). In dense interstellar environments, PAHs are likely to condense onto or integrate into water ice mantles covering dust grains, where they can be pro- cessed by UV photons. Understanding the role of ice in the photo-induced processing of adsorbed or embedded PAHs is therefore a key issue in astrochemistry. We present a study of various PAHs (anthracene, pyrene and coronene) embedded in or adsorbed on four types of water ice (amorphous and crystalline), combining FTIR spectroscopy with theoretical approaches (SCC- DFTB and MD). Our results highlight the role of the structure of ice on the photo-reactivity of PAHs with water. The influence of ice structure on the adsorption and ionisation energies of PAHs is discussed in the light of previous experimental and theoretical studies. Noble, J. A.; Jouvet, C.; Aupetit, C.; Moudens, A.; Mascetti, J. “Efficient photochemistry of coronene:water complexes” A&A 2017, 599, A124 Michoulier, E.; Noble, J. A.; Simon, A.; Mascetti, J.; Toubin, C. “Adsorption of PAHs on interstellar ice viewed by classical molecular dynamics” PCCP 2018, 20, 8753 Michoulier, E.; Ben Amor, N.; Rapacioli, M.; Noble, J. A.; Mascetti, J.; Toubin, C.; Simon, A. “Theoretical determination of adsorption and ionization energies of polycyclic aromatic hydro- carbons on water ice” PCCP 2018, 20, 11941

Coronene on Low Density Amorphous Ice kJ/mol z

Figure 1: Coronene adsorption on LDA: MD simulation (left), and energy map (right)

48 On the gas-phase formation of the HCO radical: accurate quantum study of the H+CO radiative association

T. Stoecklina, P. Halvicka, H.-G. Yub,c, G. Nymanb, Y. Ellingerd aInstitut des Sciences Moleculaires, Universite de Bordeaux, France; bDepartment of Chemistry and Molecular Biology, University of Gothenburg, Sweden; cOn leave from Brookhaven National Laboratory, USA; dUniversite Pierre-et-Marie-Curie, France; Contact: [email protected]

The roles of gas-phase and gas-grain processes in the interstellar medium (ISM) are important to know for understanding the chemical evolution of the ISM. In this work we investigate the formation of HCO through radiative association. In radiative association two species collide and during the collision a photon is emitted, which carries away enough energy that the fragments stick together and end up in a bound state of the forming molecule. The emission of the photon is an improbable event giving small cross sections for molecule formation through radiative association. However, since the ISM is so dilute, energy loss by three-body collisions are even less likely. Thus radiative association can still be an important process for forming new molecules, particularly in dust poor regions. Successful experimental measurements of radiative association rate constants are very few due to the very small cross sections. It is thus of interest to make theoretical calculations to estimate these rate constants. Here we perform quantum dynamical calculations of the radiative associ- ation cross sections and rate constants for the formation of HCO through radiative association. HCO may be an important species in the formation of complex organic molecules in space. It has for instance been proposed that a possible route to methanol could be

CO → HCO → H2CO → H3CO → H3COH To investigate the first step in this mechanism we employ a recent 3D potential energy surface for HCO which is based on high level ab initio calculations and we perform new ab initio calculations to obtain the 3D dipole moment surfaces that we require. We then perform quantum dynamics calculations for several values of the total angular momentum, but a J-shifting procedure is used to obtain reaction probabilities for additional J-values allowing us to obtain the cross sections and rate constants. The thermal rate constants that we calculate are so small that the gas-phase H+CO radiative association in a cold interstellar medium cannot be the process in the first step of the sequence shown above leading to the formation of methanol.

49 Hydrogenation of Isocyanic acid on Water Ice Surfaces: a Computational Approach

P. Redondoa, C. Barrientosa, A. Largoa

aComputational Chemistry Group, Departamento de Qu´ımica F´ısica y Qu´ımica Inorg´anica, Facultad de Ciencias, Universidad de Valladolid, 47011 Valladolid, Spain Contact: [email protected]

Formamide, NH2CHO, the simplest molecule with a peptide bond (NH-C=O), is expected to play a key role in the origin of life. In this way, formamide may provide all the components necessary for the formation of nucleic acid bases, carboxylic acids, sugars, and amino acids, under prebiotic conditions. The origin of formamide in the interstellar medium is not yet well established and is still an open question. Different theoretical and experimental works have been devoted to the formamide formation through gas-phase reactions or on the surface of interstellar grains, these last through surface reactions or induced by energetic processes. L´opez-Sepulcre et al. (2015, MNRAS, 449, 2438) detected isocyanic acid, HNCO, and NH2CHO in five sources and found a linear correlation between their abundances. This suggests that the two species are chemically related and they propose that NH2CHO could be formed on the mantles of dust grains by hydrogenation of HNCO. In this work, we report the results of theoretical calculations (using ab initio and density func- tional theory methods) on the hydrogenation reactions of isocyanic acid: HNCO + H2 and HNCO + 2H, taking or not taking into account the involvement of an existing water ice support all along the reaction path. The calculations are performed using a cluster approach of different sizes. To select the DFT method employed for large size clusters we consider as reference treatment standard post Hartree-Fock second-order perturbation MP2 treatments and coupled cluster cal- culations using single, double and triple excitations within the CCSD(T) formalism that taken into account correlation/dispersion effects. For the characterization of the stationary points located on each potential surface as minima or transition states, a vibrational analysis has been carried out.

Figure 1: Reaction profile for HNCO + 2H at the M062X/aug-cc-pVTZ//M062X/6- −1 31++G(d,p) level in presence of a layer of H2O (Relative energies in kcal mol ; ZPE included.

50 Sulfur-bearing species as tracers of protoplanetary disk physics and chemistry

D. Semenova,b C. Favrec D. Fedelec S. Guilloteaud,e R. Teaguef Th. Henninga A. Dutreyd,e E. Chapillong F. Hersantd,e V. Pi´etug

aMax-Planck-Institut f¨ur Astronomie, K¨onigstuhl17, D-69117 Heidelberg, Germany bDepartment of Chemistry, Ludwig Maximilian University, Butenandtstr. 5-13, D-81377 Munich, Germany cINAF, Osservatorio Astrofisico di Arcetri, L.go E. Fermi 5, I-50125 Firenze, Italy dLAB, Universit´ede Bordeaux, B18N, All´eeGeoffroy, Saint-Hilaire, CS 50023, 33615 Pessac Cedex eCNRS, Universit´ede Bordeaux, B18N, All´eeGeoffroy, Saint-Hilaire, CS 50023, 33615 Pessac Cedex f Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, MI 48109, USA gIRAM, 300 Rue de la Piscine, F-38046 Saint Martin d’H`eres, France Contact: [email protected]

Several sulfur-bearing molecules are observed in the interstellar medium and in comets, in strong contrast to protoplanetary disks where only CS, H2CS, and SO have been detected so far. We combine observations and chemical models to constrain the sulfur abundances and their sen- sitivity to physical and chemical conditions in the DM Tau protoplanetary disk. We obtained 0.500 Atacama Large Millimeter Array observations of DM Tau in Bands 4 and 6 in lines of CS, SO, SO2, OCS, CCS, H2CS, and H2S, achieving a ∼ 5 mJy sensitivity. Using the non-Local Thermodynamical Equilibrium radiative transfer code RADEX and the forward-modeling tool DiskFit, disk-averaged CS column densities and upper limits for the other species were derived.

Only CS was detected with a derived column density of ∼ 2 − 6 × 1012 cm−2. We report a first 11 14 −2 tentative detection of SO2 in DM Tau. The upper limits range between ∼ 10 and 10 cm for the other S-bearing species. The best-fit chemical model matching these values requires a gas-phase C/O ratio of & 1 at r & 50 − 100 au. With chemical modeling we demonstrate that sulfur-bearing species could be robust tracers of the gas-phase C/O ratio, surface reaction rates, grain size and UV intensities.

The lack of detections of a variety of sulfur-bearing molecules in DM Tau other than CS implies a dearth of reactive sulfur in the gas phase, either through efficient freeze-out or because most of the elemental sulfur is in other large species, as found in comets. The inferred high CS/SO and CS/SO2 ratios require a non-solar C/O gas-phase ratio of & 1, consistent with the recent observations of hydrocarbon rings in DM Tau. The stronger depletion of oxygen-bearing S- species compared to CS is likely linked to the low observed abundances of gaseous water in DM Tau and points to a removal mechanism of oxygen from the gas.

51 Solid-Phase Cosmic Ray-Driven Radiation Chemistry in Astrochemical Models

Christopher N. Shingledeckera,b,c, Jessica D. Tennisc, Romane Le Gale, Johannes K¨astnerb, Paola Casellia, Eric Herbstc,d

aMax-Planck-Institut f¨urextraterrestrische Physik, Germany bInstitute of Theoretical Chemistry, University of Stuttgart, Germany cDepartment of Chemistry, University of Virginia, USA; dDepartment of Astronomy, University of Virginia, USA; eHarvard-Smithsonian Center for Astrophysics, USA Contact: [email protected]

Cosmic rays are known to have a significant physicochemical impact on interstellar environments [1]. Moreover, experimental studies have shown that the interaction between energetic parti- cles and low-temperature ices can result in the formation of complex [2] - even prebiotic [3] - molecules. However, modeling the chemical effects of cosmic ray collisions with interstellar dust grain ice mantles has proven challenging due to the complexity and variety of the underlying physical processes. In order to address this shortcoming and, hopefully, bridge the current gap between models and experiments, we have recently developed a theoretical framework we believe to be of general use in standard rate equations-based astrochemical models [4]. In this poster, we summarize the theory behind our method and show how it can be utilized. Furthermore, we highlight preliminary results from recent simulations of cold cores [5] showing the effect of this non-thermal, non-diffusive cosmic ray-driven ice chemistry on the abundances of several astrochemically interesting species.

References

[1] Indriolo, Nick and McCall, Benjamin J., Gas-phase astrochemistry, Chem. Soc. Rev., 42, 7763-7773, 2013

[2] Jheeta, S., Domaracka, A., Ptasinska, S., Sivaraman, B., & Mason, N. J., The irradiation of pure CH3OH and 1:1 mixture of NH3:CH3OH ices at 30 K using low energy electrons, Chem. Phys. Lett., 556, 359-364, 2013

[3] Holtom, P. D., Bennett, C. J., Osamura, Y., Mason, N. J., & Kaiser, R. I., A combined exper- imental and theoretical study on the formation of the amino acid glycine (NH2CH2COOH) and its isomer (CH3NHCOOH) in extraterrestrial ices, Ap. J., 626, 940-952, 2005 [4] Shingledecker, C. N. & Herbst, E., A general method for the inclusion of radiation chemistry in astrochemical models, Phys. Chem. Chem. Phys., 20, 5359-5367, 2018

[5] Shingledecker, C. N., Tennis, J. D., Le Gal, R., Herbst, E., On Cosmic Ray-Driven Grain Chemistry in Cold Core Models, Ap. J., 861, 1-20, 2018

52 Interstellar carbon dust analogs obtained using plasma based processes

I. C. Gerbera, B. C. Hodoroabaa, D. Ciubotarua, A. Chipera, V. Pohoataa, I. Mihailab, I. Topalaa

aFaculty of Physics, Iasi Plasma Advanced Research Center (IPARC); bIntegrated Center of Environmental Science Studies in the North-Eastern Development Region (CERNESIM), Alexandru Ioan Cuza University of Iasi, Blvd. Carol I No. 11, Iasi, 700506, Romania Contact: [email protected]

The carbonaceous materials in the interstellar medium are known to play a role in comet and star formation, molecular catalysis, UV and optical radiation reprocessing, etc. The interstellar dust particles have been studied using numerous space probes and infrared absorption measurements, the results being still unable to fully explain the composition, structure and properties of the interstellar medium. The study of interstellar dust is carried out by analysis of molecules and ions reactions in gas phase and/or on grain surfaces, interaction of dust grains with different radiation fields, production and analysis of various laboratory carbon dust analogs, etc. The plasma based techniques, using hydrocarbon gases as precursors, can be employed to grow sub-micrometer carbon particles showing spectroscopic features consistent with the interstellar medium. Our study proposes a comparative analysis of plasma based deposition methods, designed for dust analog synthesis: the dielectric barrier discharge (DBD), the radio-frequency (RF) discharge and the pulsed laser deposition (PLD). Electrical parameters are monitored during the deposition process, mass spectrometry is used to study the ions present in plasma volume and their energy distribution function, in situ optical measurement is carried out to monitor the excited species and FTIR gas phase spectra are used to detect the hydrocarbon species. The analogs were characterized using multi spectroscopic techniques (FTIR, UV, XPS). Furthermore, the optical microscopy investigations (Figure 1) allows a comparison of our car- bonaceous products and the interstellar dust particles, as revealed by recent observation on planetary, asteroidal and cometary dust: the grains or aggregates porosity and geometrical fea- tures (dimensions of particles, irregularity). Also, spectroscopic features can be extracted and compared with observational data or theoretical modelling of data from galactic (Sgr A*), extra galactic objects (IRAS 08572+3915, IRAS 19254−7245, NGC 1068 and NGC 5506), or objects that show a rich content of sp3 hybridized carbon.

Figure 1: Top line: typical photos of the discharges during the deposition process; Bottom line: optical microscopy images of the dust analogs obtained on flexible graphite substrate.

53 Absolute intensities and photolytic behaviour of ethyl mercaptan (HS-CH2CH3) and dimethyl sulfide (CH3-S-CH3) in Ar and in CO

J. Zapala a, M. Gronowskia, T. Custera

aInstitute of Physical Chemistry of the Polish Academy of Sciences, Poland Contact: [email protected]

Ethyl mercaptan (HS-CH2CH3) and dimethyl sulphide (CH3-S-CH3), compounds of potential astrochemical interest, have been investigated by means of IR spectroscopy. Compounds were suspended in argon (Ar) and in carbon monoxide (CO) matrixes at 6K. From interference fringes in IR spectra, matrix thicknesses were calculated and from these thicknesses, absolute intensities values for each vibration in both environments were estimated. Deposited matrixes were exposed to UV radiation using an ArF excimer laser (194nm) and hydrogen lamp (121nm) in separate experiments for each combination of compound / medium. Photolytic products were similar for CH3-S-CH3 in Ar and in CO and consisted of large amounts of CH4 and CH2S as well as smaller amounts of various CnS (n=1-4) species. HS-CH2CH3 photolysis also produced mainly CH4 and CS, however, methanethiol was also a main product. Additionally, small amounts of ethane, ethene and ethyne could be distinguished in the spectra. Lastly, thermal annealing was performed for each compound/medium/light-source combination. The emission originating from sulphur recombination was observed for all samples photolysed by the ArF excimer laser but not the hydrogen lamp.

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