Microwave and infrared spectra of urethane Roman A. Motiyenko, Manuel Goubet, Justin Habinshuti, Therese H. Huet Laboratoire PhLAM, Universite Lille 1, 59655 Villeneuve d’Ascq Cedex, France Eugen A. Alekseev Institute of Radio Astronomy of NASU, 4, Chervonopraporna str., Kharkov, Ukraine Pierre Asselin, Pascale Soulard Universite Pierre et Marie Curie, Bat. F74 - Case 49, 4 place Jussieu, F- 75252, Paris Cedex 05, France

Urethane (ethyl carbamate) Two lowest-energy conformers: I and II Important astrophysical precursors: NH3 and C2H5OH Possible carcinogen and is present in some alcoholic beverages, therefore should be controlled Conformer I Previous study: K. M. Marstokk and H. Mollendal, Acta Chem. Scandinavica, vol. 53, 329-334 (1999) Microwave spectra of the conformers I and II of urethane in 16.5 – 56 GHz frequency range 14N hyperfine structure was not resolved → relatively large errors for this frequency range ~0.1 MHz MP2/cc-pVTZ and B3LYP/6-31G* ab initio calculations Conformer II

MWFT spectroscopy Microwave Fourier transform spectrometer with a pulsed supersonic jet. Spectra were obtained in the frequency range 5 – 20 GHz. The spectral resolution about 10 kHz allowed to study nuclear quadrupole and spin-spin hyperfine structures Carrier gas P= 1.5 bars (Ne) Inside the cavity… (not at the scale) Heated nozzle T= 373±2 K Mirror Urethane

Conformer I reassignment Basis for predictions: K. M. Marstokk and H. Mollendal, Acta Chem. Scandinavica, vol. 53, 329-334 (1999) (*) Q-type transitions were easily assigned Problems with R-type transitions. Lines are not in their positions ± 10 MHz!!! According to (*): A=8999.137 MHz B=2146.270 MHz C=1776.159 MHz 111 ← 000 : A+C = 10775 MHz 10755 MHz 212 ← 101 : A+3C = 14327 MHz 14288 MHz Reason: Wrong assignment of weak aR-type in (*) a ~ 0.6 D A=8989 MHz B=2136 MHz C=1766 MHz !!!

Hyperfine structure

MW conventional spectroscopy MW spectrometer in Kharkov Frequency range in this study: 50 – 150 GHz Resolution: 50 – 100 kHz – hyperfine structure is partially resolved Precision in this study: 10 kHz MW spectrometer in Lille Frequency range in this study:150 – 250 GHz Resolution: 100 – 300 kHz – hyperfine structure is not resolved Precision in this study: 20 – 40 kHz No heated absorbing cell available → the sample was heated only up to 313 K.

MW spectrometer in Kharkov BWO, 50 – 150 GHz PLL IF = 25 MHz FM modulated synthesizer 25 MHz Klystron 3.4 – 5.2 GHz IF = 5 MHz Absorbing cell Amplifier Lock-in detector Sine wave synthesizer 7 – 120 KHz DAC DDS AD9851 30 – 60 MHz Band-pass amplifier 390-430 MHz Synthesizer 360 MHz Frequency divider f/2 Frequency Doubler (optional) Detector Schottky Reference synthesizer 390-430 MHz

MW spectrometer in Lille BWO power source BWO Bolometer Absorbing cell PLL IF = 312 – 328 MHz Amplifier Fmod=5 kHz Synthesizer НР 3326В 9.75-10.25 MHz Synthesizer НР 83711В 2 – 20 GHz Lock-in detector GPIB bus PLL lock control GPIB controller ADC ADuC 834

Microwave spectra (Kharkov) The strongest lines correspond to Ka = 11← 10 series of bQ1,-1 transitions of conf. II

Microwave spectra (Lille) The series of Ka = 20← 19 series of bQ1,-1 transitions of conf. II is well observable

MW results for conformer I Rotational parameters (A-reduction) Hyperfine structure parameters Ground state va=1 va=2 A, MHz 8989.50716(13) 8936.229(13) 8878.016(78) B, MHz 2136.621922(25) 2136.7518(14) 2137.4564(65) C, MHz 1766.526154(25) 1770.72478(19) 1776.06521(17) ΔJ, kHz 0.178197(13) 0.1882(18) 0.2215(77) ΔJK, kHz 1.236634(98) 1.246(94) 1.25(18) ΔK, kHz 5.2602(15) 6.18(10) 7.05(39) δJ, kHz 0.0346687(32) 0.03533(10) 0.04287(37) δK, kHz 0.64633(18) 0.499(65) 1.534(33) HJ, Hz 0.0000259(26) HJK, Hz -0.00130(12) HKJ , Hz -0.03086(47) HK, Hz 0.0387(50) hJ, Hz 0.0000108(10) hJK, Hz -0.000743(95) hK, Hz 0.0208(28) Nlines 962 138 120 RMS, MHz 0.0128 0.0069 0.0070 Quadrupolar GS va=1 va=2 χaa, MHz 2.1171(13) 1.25(85) 1.47(53) χbb, MHz 2.1665(29) 2.5(13) 2.54(87) χcc, MHz -4.2836(16) -3.82(47) -4.01(34) Spin-spin GS 3/2Daa, kHz -40.3(24) 3/2Dbb, kHz 14.0(63) 3/2Dcc, kHz 26.3(39)

MW results for conformer II Rotational parameters (A-reduction) Hyperfine structure parameters Ground state vt=1 va=1 A, MHz 7565.417996(90) 7551.7041(11) 7606.0885(17) B, MHz 2414.784375(28) 2397.83275(49) 2407.22405(54) C, MHz 2116.375036(34) 2105.34650(31) 2115.79939(68) ΔJ, kHz 0.916104(20) 1.16722(49) 0.81391(50) ΔJK, kHz 0.38570(10) 1.4546(16) -0.1609(33) ΔK, kHz 12.55849(59) 11.009(13) 14.496(22) δJ, kHz 0.0838211(62) 0.12025(20) 0.060494(88) δK, kHz -3.49567(65) -7.9403(21) -2.385(11) HJ, Hz -0.0013315(44) HJK, Hz -0.00512(13) -0.01004(17) 0.00879(11) HKJ , Hz -0.09992(39) -0.122(17) -0.0844(29) HK, Hz 0.08545(98) hJ, Hz -0.0007311(15) hJK, Hz 0.08097(47) hK, Hz 0.6947(28) Nlines 1121 240 145 RMS, MHz 0.0124 0.0153 0.0101 Quadrupolar GS vt=1 va=1 χaa, MHz 1.8921(11) 2.17(59) 1.38(54) χbb, MHz 1.8922(22) 1.72(88) 2.16(83) χcc, MHz -3.7843(11) -3.89(29) -3.54(29) Spin-spin GS 3/2Daa, kHz -61.4(15) 3/2Dbb, kHz 34.7(31) 3/2Dcc, kHz 26.7(16)

Ab initio structure Conformer I Conformer II A (MHz) B (MHz) C (MHz) a (Deb.) b (Deb.) c (Deb.) MP2/ 6-311++G(3df,2p) 9007.9 2151.9 1776.2 0.63 2.51 0.61 7588.5 2443.5 2133.1 0.07 2.28 1.06 aug-cc-pVDZ 8835.4 2118.2 1747.7 -0.66 -2.48 0.69 7423.1 2411.8 2102.4 -0.01 -2.23 1.16 aug-cc-pVTZ 8984.4 2148.1 1773.0 0.65 2.48 0.67 7571.7 2439.6 2127.9 0.01 2.25 1.11 cc-pVQZ 9028.5 2158.0 1781.3 0.60 0.68 7612.0 2448.3 2136.6 0.05 1.12 Experiment 8989.5 1766.5 7565.4 2414.8 2116.4 In case of long range interactions addition of diffuse functions makes calculations more precise

Conformational stability According to H. Mollendal Conformer I is found to be 0.12(12) kcal/mol more stable than Il by relative intensity measurements. MP2/ 6-311++G (3df,2p) aug-cc-pVDZ aug-cc-pVTZ cc-pVQZ E(MP2) E(MP2) – ZPE Conf. I, kcal/mol -202799.14 -202640.18 -202805.36 -202737.15 -202855.75 Conf. II, kcal/mol -202799.24 -202640.39 -202805.46 -202737.16 -202855.83 I–II, kcal/mol 0.10 0.21 0.01 0.08

IR spectra assignment (preliminary) Spectral range: 1000 – 1900 cm-1 Resolution: 0.1 cm-1 Conformer I Conformer II  MP2/aug-cc-pVTZ Exper. I (km/mol) n (cm-1) 15 140.7 1126.7 1078 19 425.1 1353.0 1333 20 62.0 1412.4 1379 25 119.4 1623.2 1580 26 410.2 1806.9 1778  MP2/aug-cc-pVTZ Exper. I (km/mol) n (cm-1) 16 111.3 1136.1 1107 18 20.0 1342.3 1267 19 353.8 1358.3 1330 20 54.2 1408.7 1375 21 25.5 1431.9 1401 25 121.0 1621.8 1580 26 392.1 1805.3 1769

Acknowledgements PEPCO-NEI network (project nr 509031H) INTAS (YSF grant, ref. nr 06-1000014-5984) PhLAM laboratory and G. Wlodarczak

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