Complex Organic Chemistry in Interstellar Ices
Susanna L. Widicus Weaver Department of Chemistry Emory University 2 atoms 3 atoms 4 atoms 5 atoms 6 atoms 7 atoms 8 atoms 9 atoms 10 atoms 11 atoms 12 atoms 13 atoms
H2 C3 c-C3H C5 C5H C6H CH3C3N CH3C4H CH3C5N HC9N C6H6 HC11N
AlF C2H l-C3H C4H l-H2C4 CH2CHCN HC(O)OCH3 CH3CH2CN (CH3)2CO CH3C6H C2H5OCH3
AlCl C2O C3N C4Si C2H4 CH3C2H CH3COOH (CH3)2O (CH2OH)2
C2 C2S C3O l-C3H2 CH3CN HC5N C7H CH3CH2OH CH3CH2CHO
CH CH2 C3S c-C3H2 CH3NC CH3CHO H2C6 HC7N
+ CH HCN C2H2 H2CCN CH3OH CH3NH2 CH2OHCHO C8H
CN HCO NH3 CH4 CH3SH c-C2H4O l-HC6H CH3C(O)NH2
+ + – CO HCO HCCN HC3N HC3NH H2CCHOH CH2CHCHO C8H
+ + + – CO HCS HCNH HC2NC HC2CHO C6H CH2CCHCN C3H6
+ CP HOC HNCO HCOOH NH2CHO
SiC H2O HNCS H2CNH C5N
+ HCl H2S HOCO H2C2O l-HC4H
KCl HNC H2CO H2NCN l-HC4N
NH HNO H2CN HNC3 c-H2C3O
NO MgCN H2CS SiH4 H2CCNH
+ + NS MgNC H3O H2COH
+ – NaCl N2H c-SiC3 C4H
OH N2O CH3
PN NaCN
SO OCS
+ SO SO2 SiN c-SiC Detected Interstellar Molecules 2
SiO CO2
SiS NH2
+ CS H3
HF H2D+, HD2+
SH SiCN
HD AlNC
FeO SiNC
O2 HCP
CF+
SiH
PO Schematic of a Hot Core
T (gas) = 200 - 1000 K T (dust) ~90 K ~60 K ~45 K ~20 K
CO2 complex organics CO H2O, CH3OH, NH3 N2 H S O SiO 2 CH3OH 2 ice ice CH3CN CO2 ice trapped UV CO
H2O ice Hot Core
~1016 cm ~5x1017 cm CSO Orion Spectrum
5365 lines observed
79% of the lines are unassigned!
Blake et al. ApJ, 1986: RMS = 150 mK, integration time ~ 27 nights Our survey: RMS = 20 mK, time ~ 4 nights See poster by Radhuber et al. for more information! THz Observational Astronomy Stratospheric Observatory for Herschel Infrared Astronomy Observatory Launched on Flight tests began in 2007 May 14, 2009! Initial science observations begin in 2010 480 GHz -1.2 THz 500 GHz – 2.1 THz 1.4 – 1.9 THz
Atacama Large Millimeter Array First antennas arrived in 2007 Scheduled for completion in 2012 80 GHz – 950 GHz 64 antennas Organic Material in Meteorites
The Murchison Meteorite
• amino acids
• sugars and polyols
• other organics
http://www.hermann-beer-ka.de/nucleosynthesis/abund/Murchison.jpg Possible Molecular Formation Schemes
vs.
Key Questions: How far can chemistry go in the ISM?? Is a parent body required?? GrainGas PhaseSurface Reactions Reactions
H H H H O O O O CH3OH2+ + HCOOH C H N C + + or H3 H N C -H3O H N C H H H H H H H H H
protonated aminomethanol aminomethanol glycine
Charnley, S. (2001) Interstellar Organic Chemistry. In: The Proceedings of the Workshop The Bridge Between the Big Bang and Biology, (Consiglio Nazionale delle Ricerche, Italy). The Methyl Formate Problem • Cannot form by ion-molecule reactions Horn et al. 2004, ApJ 611, 605 • Grain surface formation? Structural isomers would have similar abundances! H H O H3C OH HO C CH3 C C C O O O H H Methyl Formate Acetic Acid Glycolaldehyde 52 2 1 • Complex molecules observed in regions of grain mantle disruption:
Shocked regions in the GC (Martin-Pintado et al.) Hot Corinos (Ceccarelli, Caselli, et al.)
Bottinelli et al. ApJL 617, 2004 Grain Surface Formation
H2O + hν OH + H CH3O hν H2 + O
CH3OH + hν CH3 + OH
HCOOCH3 CH3O + H CH2OH + H HCO NH3 + hν NH2 + H H2O, CO, CH3OH, NH3 , H2CO Ice mantle H2CO + hν HCO + H
HCO + CH3O CH3OCHO (methyl formate)
HCO + CH2OH HOCH2CHO (glycolaldehyde)
Garrod, Widicus Weaver, & Herbst, ApJ 682, 2008 Two-Stage Hot Core Model
1. Cloud Collapse (isothermal free-fall)
106 years
Previous Models
3 -3 7 -3 nH = 3x10 cm nH = 1x10 cm
2. Warm-up (secondTemperature -order power law)New Model
5x10time4 years
(high mass) 10 K 200 K Garrod, Widicus Weaver, & Herbst, ApJ 682, 2008 Initial Results: Ice Composition
-3 Sgr B2(N-LMH) (Observed) -4 -5 Model
) -6 H -7 -8 log(n/n -9 -10 -11 -12
ethanol methanol acetic acid formic acid formamide formaldehyde acetaldehyde methylamine glycolaldehyde ethylene glycol methyl formatedimethyl ether
Garrod, Widicus Weaver, & Herbst, ApJ 682, 2008 Lingering Questions 1. Methanol photolysis branching ratios? Quantitative lab measurements.
2. ID of key intermediates to trace chemistry? Laboratory studies to support observational search.
3. Varying physical and chemical parameters for interstellar clouds? Spectral line surveys of many sources.
4. Spectral interference from “interstellar weeds?” Complete laboratory spectral cataloging. Motivation: Understanding COMs in the ISM Grain surface formation hν • Simple molecules form in ice via single-atom addition reactions
• Organic radicals form in ice via photolysis of simple molecules H2O, CO, CH3OH, NH3 , H2CO • Radicals react during warm-up Ice mantle to form larger organics H H H O O CH3OH2+ + H N C + Gas phase formation or H3 H N C H H H H H H • Molecules are released from ices protonated aminomethanol aminomethanol H • Gas-phase molecules are ionized O O HCOOH C
• Ion-molecule reactions drive -H2O H N C H gas-phase organic chemistry H H glycine Transient molecules are the driving forces for both grain-surface and gas-phase chemistry. 2 atoms 3 atoms 4 atoms 5 atoms 6 atoms 7 atoms 8 atoms 9 atoms 10 atoms 11 atoms 12 atoms 13 atoms
H2 C3 c-C3H C5 C5H C6H CH3C3N CH3C4H CH3C5N HC9N C6H6 HC11N
AlF C2H l-C3H C4H l-H2C4 CH2CHCN HC(O)OCH3 CH3CH2CN (CH3)2CO CH3C6H C2H5OCH3
AlCl C2O C3N C4Si C2H4 CH3C2H CH3COOH (CH3)2O (CH2OH)2
C2 C2S C3O l-C3H2 CH3CN HC5N C7H CH3CH2OH CH3CH2CHO
CH CH2 C3S c-C3H2 CH3NC CH3CHO H2C6 HC7N
+ CH HCN C2H2 H2CCN CH3OH CH3NH2 CH2OHCHO C8H
CN HCO NH3 CH4 CH3SH c-C2H4O l-HC6H CH3C(O)NH2
+ + – CO HCO HCCN HC3N HC3NH H2CCHOH CH2CHCHO C8H
+ + + – CO HCS HCNH HC2NC HC2CHO C6H CH2CCHCN C3H6
+ CP HOC HNCO HCOOH NH2CHO
SiC H2O HNCS H2CNH C5N
+ HCl H2S HOCO H2C2O l-HC4H
KCl HNC H2CO H2NCN l-HC4N
NH HNO H2CN HNC3 c-H2C3O
NO MgCN H2CS SiH4 H2CCNH
+ + NS MgNC H3O H2COH
+ – NaCl N2H c-SiC3 C4H
OH N2O CH3
PN NaCN
SO OCS
SO+ SO 2 Detected Interstellar Molecules SiN c-SiC2
SiO CO2
SiS NH2
+ CS H3
+ + HF H2D , HD2
SH SiCN
HD AlNC
FeO SiNC
O2 HCP CF+ Radicals and Ions SiH
PO Production Methods • Small quantities (low efficiency)
• High temperatures = weak signals
• Interference from stable molecules Discharges • Reactivity/instability of products
hν
Photolysis Matrix Isolation
Supersonic Expansions High-Sensitivity Cavity-Enhanced Spectroscopy
~2 – 50 GHz
> 1000 cm-1 The ‘THz Gap’
3 GHz 30 GHz 300 GHz 3 THz 30 THz 300 THz 3000 THz 0.1 cm-1 1 cm-1 10 cm-1 100 cm-1 1000 cm-1 10,000 cm-1 100,000 cm-1
FTMW THz CRDS
10 cm 1 cm 1 mm 100 µm 10 µm 1 µm 100 nm Laboratory Spectral Cataloging First light April 1, 2009!
To Computer VDI Multiplier chain 50 GHz – 1.2 THz Detector 1 – 50 GHz Frequency Gas Flow Cell Synthesizer Sample Input To Vacuum Pump
Methanol Ethyl Cyanide CRDS High Finesse Cavity
R ~99.99%
Radiation Supersonic Detector Source Source
Mode Matching Optics
cavity ringdown recorded
IR mirrors → dielectric coated THz mirrors → metal coated Losses due to transmission Losses due to skin depth FTMW High Finesse Cavity
R ≈ 98% Supersonic Aperture: r << λ Source Radiation Source Switch
X
Detector
free-induction decay recorded microwave mirrors → aperture THz mirrors → ? Large λ, small losses Small λ, large losses with any aperture! Proposed THz-CRDS Spectrometer
HEB Detector Off-Axis Parabolic Mirror
Supersonic Source
Wire Grid To Computer Polarizers
Mode Matching Transmission = 10-4 Optics ≤700 GHz R = 99.99%
VDI multiplier chain 1 – 50 GHz 50 GHz – 1.2 THz Frequency Synthesizer Progress Toward THz-CRDS Beam profiling completed, mode-matching optimized
Polarizer reflectivity tested up to 300 GHz
R = 99.9 – 99.99% Benchtop THz-CRDS Setup Cavity Modes at 180 GHz!
Cavity length = 33 cm Mode FWHM = 1.7 MHz Polarizer R =0.988 Cavity FSR = 445.5 MHz
Need longer cavity, higher R for CRDS! Next Steps in THz-CRDS Development
• Narrow cavity modes, increase pathlength
• Incorporate translation stage; trigger ringdown events
• Extend system to higher frequencies
• Incorporate cavity into vacuum chamber
• Test fully-integrated system on known molecules
• Begin molecular spectroscopy on ions, reactive organic intermediates
• Extend to broadband spectral acquisition Using THz Spectroscopy to Trace Prebiotic Chemistry in Space Grain Surface Formation
H2O + hν OH + H hν H2 + O
CH3OH + hν CH3 + OH CH3O + H CH2OH + H
NH3 + hν NH2 + H H2O, CO, CH3OH, NH3 , H2CO Ice mantle H2CO + hν HCO + H
HCO + CH3O CH3OCHO (methyl formate)
HCO + CH2OH HOCH2CHO (glycolaldehyde)
Garrod, Widicus Weaver, & Herbst, ApJ 682, 2008 Methanol Dissociation
• • • • • •
• Energy (kcal/mol) Energy
Chang and Lin 2004, Chem. Phys. Lett., 384, 229 THz Spectroscopy as a Probe
Mass Spec alone cannot distinguish products
THz spectroscopy can!
See poster by Laas et al. for more information! Astrochemical Modeling • A series of methanol photolysis branching ratios were used, and peak abundances were compared to Sgr B2(N) abundances
• Ice photolysis branching ratios of CH3:CH2OH:CH3O = 18:1:1 give the best match to Sgr observations
• Longer warm-up timescales give better agreement with observed abundances of more complex organic species. H H H H . H C. O C H + C O O C O H H H H H H
methoxymethanol
H H H H H C O Prebiotic + . O. O C O H H Molecule Formation H methanediol
H H H O C. H N. + H N C H H O H H H aminomethanol H H H H C H C H H O C O O C H H H H O(1D) H
dimethyl ether methoxymethanol
H H H 1 H O O O( D) Insertion O C C H H Reactions O(1D) H H methanol methanediol O(1D) H H O
H N C H N C H H H H H H
methylamine aminomethanol Photolysis Fast-Mixing Nozzle
N2O + Ar
hν O(1D) quartz capillary
CH3OH
1 O( D) + CH3OH → HOCH2OH Interaction region
See poster by Anderson et al. for HOCH2OH Kinetics Studies more information! + Ar Initial Photlysis Results: N2O
Photolysis N2O photolysis monitored by Fast-Mixing Source rotational line signal depletion hν
mm/submm
12% reduction in
N2O signal observed Using THz Spectroscopy to Trace Prebiotic Chemistry in Space
What do we plan to measure? • Photolysis branching ratios for complex organics • Spectra of small, reactive organics produced via O(1D) insertion • Spectra of molecular ions with complex internal motion • THz spectral catalogs of “interstellar weeds” Acknowledgements
The Widicus Weaver Group: Mary Radhuber, Jake Laas, Brandon Carroll, Brett McGuire, Thomas Anderson Jay Kroll, Patrick Lanter
Eric Herbst, OSU Robin Garrod, Cornell Geoffrey Blake, Caltech Thom Orlando, GA Tech CSO/Caltech: Matthew Sumner, Frank Rice, Jonas Zmuidzinas, & Tom Phillips
Virginia Diodes, Inc. QMC Instruments, Ltd.