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Methylimino Acetonitrile CH SUBMILLIMETER WAVE SPECTROSCOPY FOR ISM:IMINES WITH INTERNAL ROTATION L. Margulès1, R. A. Motiyenko1, O. Dorovskaya2,V.V. Ilyushin2, B.A. Mc Guire3, A. Remijan3 and J.C. Guillemin4 1Laboratoire PhLAM UMR8523,Université de Lille, France 2Institute of Radio Astronomy of NASU, Kharkiv, Ukraine 3National Radio Astronomy Observatory, Charlottesville, VA, USA 4Institut des Sciences Chimiques de Rennes, ENSCR, France L. Margulès et al, 74TH International Symposium on Molecular Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS ISM Imines Targets • This imine could have played some role in prebiotic chemistry (Xiang Y.-B. et al., Helvetica Chimica Acta 1994, 77(8), 2209) • The aldimines are important to understand amino acids formation process as they appear in reaction scheme of Strecker-type synthesis. • Major question: How define “good target”? Most of the time related to molecules detected yet! • The three molecules presented here, follow the reasoning based on the 3 possible pathways L. Margulès et al, 74TH International Symposium on Molecular 2 Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS ISM Imines Targets • 1) Going to next complexity : apply it to “imines…” during our measurements!! (idea not so stupid…) Propanimine (L. Margulès et al., RI07, 2015, 70th ISMS) Ethanimine’s work still usefull: spectrosocopic studies limited to low Ka, usefull to line prediction, intensities calculations L. Margulès et al, 74TH International Symposium on Molecular 3 Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS ISM Imines Targets • 2) Substitution in detected molecules : • replacing atom (O with S for exemple) • Group, etc… Methylimino acetonitrile CH3N=CHCN Many methylated derivatives of detected compounds have been observed in the ISM : good candidate for the ISM since the corresponding unsubstituted imine HN=CHCN, a dimer of hydrogen cyanide, has been detected in 2013 in this medium (D. P. Zaleski, et al., 2013, ApJL, 765:L9) • 3) isomers of detected molecules : N-Methylmethanimine CH3N=CH2: ethanimine’s isomer % Success is pretty low, more about targets’s choice in RG08 L. Margulès et al, 74TH International Symposium on Molecular 4 Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS Ethanimine: CH3CHNH – Stark spectroscopy • up to 140 GHz: Econf g.s., vt=1 and Zconf g.s. (Lovas et al., J. Chem. Phys. 72, 4964, 1980) • from 18 to 76 GHz: Zconf g.s. and vt=1(Brown et al., AJCh, 33, 1, 1980) – Zeeman MW (Krause et al., Z. Naturfosch. 46, 785, 1991) – CP-FTMW measurements from 6.5 to 40 GHz (Loomis et al., ApJL, 765, L9, 2013) – MM measurements up to 300 GHz, limited to low Ka (Melli et al.APJ 855, 123, 2018) Z conf (trans) DEa = 282 cm-1 E conf (cis) m = 2.380 D ma= 0.834 D a m = 0.445 D mb= 1.882 D b Zconf spectra could be more intense even at ISM temperature aab initio calculation at MP2/aug-cc-pvqz level including ZPE correction TH 5 L. Margulès et al, 74 International Symposium on Molecular Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS Methylimino-acetonitrile • No spectroscopie studies available up to now • 2 conformers: E and Z Z conf E conf DE = 124.44 cm-1 DE =1.489 kJ/mol ma= 4.12 D ma= 2.01 D mb= 2.07 D mb= 0.47 D mc= 0.00 D mc= 0.00 D • Econf is the most stable • At lab temperature, Boltzman factor is 0.55 for Zconf but its dipole moment is smaller than Econf one spectra of Zconf much weaker L. Margulès et al, 74TH International Symposium on Molecular 6 Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS N-Methylmethanimine • MW study up to 40 GHz (Sastry & Curl, J. Chem. Phys. 41, 77, 1964) • MM measurements up to 320 GHz (Demaison et al., J. Mol. Spectrosc. 107, 250, 1984) m = mb = 1.53 D -1 V3 = 714 cm No need for new measurements in a first step to search it in ISM, just need to « refit » and provide new prediction L. Margulès et al, 74TH International Symposium on Molecular 7 Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS Analysis of the spectra Methyl group is C3v symmetry V3 V6 V(a) = (1- cos3a)+ (1- cos6a)+... 2 2 • values of some barriers -1 1 - • Acetaldehyde: 408 cm cm • Methyl Formate: 373 cm-1 ≈756 3 V • Ethanimine: 586 cm-1 • Methylimino acetonitrile: 713 cm-1 • N-Methylmethanimine: 714 cm-1 For these imines: Even with « high barrier » A-E spliting are observed L. Margulès et al, 74TH International Symposium on Molecular 8 Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS Experimental details • Synthesis of pure sample was performed • Fast DDS Lille’s spectrometer was used to record the spectra • Fast decade spanning spectrometer:0.15-1.5 THz • Less than 24h is needed at high resolution (Doppler limited) and sensitivity to record the all range • Typical: Acq. time 1ms/point • Imines spectra: • From 75 to 660 GHz • Acq. Time: 2ms/pt • Step: 24-60 kHz • Pressure: 15-20 mbar On going developpment: emission spectroscopy (L. Zou FB04) L. Margulès et al, 74TH International Symposium on Molecular 9 Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS Ethanimine spectra E Conf Rbranch J=8-7 Z Conf 1,20 5,14 =4 =4 =4 21 =4 1,20 0,16 a a a a - =6 18 =5 =6 =5 a 19 - 21 a 16 a a - - 11 2, A: K A: K E: E: K E: E: K 19 15 6, E: E: K A: K 2, E: E: K 1, A: K E:21 A:17 A:21 E:16 147910 MHz 148010 MHz • ma:hyperfine quadrupole E/E:212, 19-211,20 Z/E:85, 3-75,2 E:85, 4-75,3 structure for high Z/A:85, 3-75,2 7 9 7 Z/A:8 -7 F"-F’ 9 Ka Values and low J 8 - 5, 4 5,3 - 8 - - 6 8 - 6 8 - 21 7 7 • mb: bigger splitting - 21 8 20 22 and K is only 1.. 7 9 a - - - 7 - - 6 8 20 22 L. Margulès et al, 74TH International Symposium on Molecular 10 Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS Ethanimine spectra Rbranch J=16-15 • Still splittings at 300 GHz and J=50 A: 312,29-311,30 294.6GHz 297.0GHz 1.35 MHz 21 22 20 - - - 20 F:21 F:22 E: 505,45-504,46 242,23-241,24 312,29-311,30 A E A E 505,45-504,46 A 283,25-274,24 E A E 0.55 MHz 51 49 - - 50 - 295205 MHz 49 294665 MHz F:51 F:50 L. Margulès et al, 74TH International Symposium on Molecular 11 Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS Methylimino-acetonitrile Spectra 481,47 – 471,46 490,49 – 480,48 spectra E A E A 0.430 MHz 0.433 MHz 230118.549 230118.979 228861.641 228862.074 54 – 53 291,29 – 280,28 0,54 1,53 E A E A 15.067 MHz 7.433 MHz 163605.200 163620.267 244499.963 244507.396 • Internal rotation effect is more important with μb transitions. Important to assign them even if they are very weak L. Margulès et al, 74TH International Symposium on Molecular 12 Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS 627169 MHz 641030 MHz 627169 MHz 157,9- 146,8 A 157,8- 146,9 A 157,9- 146,8 E 157,8- 146,9 E Q branch K a = 8 - 13 7 336,28- 325,27 E 336,27- 325,28 A 336,28- 325,27 A 627465 MHz 641690 MHz 336,27- 325,28 E Analysis of the spectra • Barrier is not the only one criteria : r vector value indicates how strong is the coupling between torsion motion and rotation. • Could be simply calculate from ab initio geometry of the molecule, XIAM code also provide it as angles with CH3 rotor -1 V3 in cm r a HCOOCH3 373 0.08 b with CH3CHO 408 0.33 c CH3OH 374 0.81 θ(i,g) :angles between CH3 group axis and inertial principal axis aV. Ilyushin et al. J. Mol. Spectrosc. 255, 32, 2009 bI. Kleiner et al. J. Mol. Spectrosc. 179, 41, 1996 cL.-H. Xu et al. J. Mol. Spectrosc. 251, 305, 2008 L. Margulès et al, 74TH International Symposium on Molecular 14 Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS Analysis of the spectra θ(i,a) :angles between CH3 group axis and a inertial principal axis Ethanimine CH3CHNH Conf. Z Conf. E BPAM BPAM Internal Internal rotation axis rotation axis APAM APAM A=49964 MHz – Ia=10.1 uA2 A=53120 MHz – Ia=9.51 uA2 r = 0.306 r = 0.287 L. Margulès et al, 74TH International Symposium on Molecular 15 Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS Analysis of the spectra θ(i,a) :angles between CH3 group axis and a inertial principal axis Methylimino acetonitrile CH3N=CHCN Conf. Z Conf. E BPAM Internal APAM rotation axis θ(i,a) = 12.0° Internal rotation θ(i,a) = 78.6° axis A=45241 MHz – Ia=11.17 uA2 A=13151 MHz – Ia=38.42 uA2 B= 3640 MHz – Ia=138.84 uA2 r = 0.306 r = 0.028 L. Margulès et al, 74TH International Symposium on Molecular 16 Spectroscopy, JUNE 17-21, 2019 - CHAMPAIGN-URBANA, ILLINOIS Analysis of the spectra θ(i,a) :angles between CH3 group axis and a inertial principal axis N-Methylmethanimine CH3N=CH2 BPAM Internal rotation axis θ(i,a) = 25.0° APAM A=52513 MHz – Ia=9.63 uA2 r = 0.301 L.
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