1 The rotational spectrum of 13 CH 3 NH 2 up to 1 THz Roman A. Motiyenko, Laurent Margulès PhLAM, Université Lille 1 Vadim Ilyushin Institute of Radio Astronomy of NASU, Kharkov

Interstellar methylamine 12 CH 3 NH 2 detected in Sgr B2 and Orion KL at 3 mm: Kaifu et al. ApJ 191 (1974) L135 in cm wave range: Fourikis et al. ApJ 191 (1974) L139 Detected in the atmosphere of Jupiter Kuhn et al. Geophys. Res. Lett. 4 (1977) 203 Precursor of glycine NH 2 CH 2 COOH CH 3 NH 2 +CO 2 mixture irradiated by UV: Bossa et al. A&A 506 (2009) 601; Lee et al. ApJ 697 (2009) 428; Holtom et al. ApJ 626 (2005) 940

Methylamine in THz domain Intense spectrum extending far beyond 1 THz Good candidate for Herschel observations (HIFI instrument 480 – 1910 GHz) T = 293 K T = 150 K T = 50 K detected in interstellar medium here

Previous studies 12 CH 3 NH 2 : more than 10 publications since 1947 Ohashi and Hougen, J. Mol. Spec (1987) – effective rotational-tunneling Hamiltonian Ilyushin et al., J. Mol. Spec (2005) – extension of the model, fit within experimental accuracy of microwave and IR data Ilyushin and Lovas, J. Phys. Chem. Ref. Data 36 (2007) – accurate predictions and intensity calculation up to 500 GHz for all transitions with J<30 Yu and Drouin, Columbus 2009 WH11 – extension of the measurements up to 1.6 THz Several deuterated species also studied: CD 3 NH 2, CD 3 ND 2, CH 3 NHD 13 CH 3 NH 2 : no spectroscopic studies

Two large amplitude motions: CH 3 torsion and NH 2 inversion -Ambiguity in barrier heights Torsional barrier: cm -1 Takagi, J. Phys. Soc. Jpn 30, 1145, 1971:684.1 cm cm -1 Kreglewski, J. Mol. Spec. 133, 10, 1989:718.4 cm cm -1 Woon, Columbus 2007, RH08:536.2 cm -1 Barrier to inversion: 1688 cm -1 Tsuboi, J. Mol. Spec. 22, 272, 1967:1688 cm cm -1 Sztraka, Acta Chim Hung 124, 865, 1987:2081 cm cm -1 Kreglewski, J. Mol. Spec. 133, 10, 1989:1943 cm cm -1 Woon, Columbus 2007, RH08:1366 cm -1

6 Tunneling splittings A 1, A 2, B 1, B 2, E 1, E 2 Each energy level is labeled by the values of usual quantum numbers J and K=K a and by an overall torsion- wagging-rotation symmetry species of G 12 PI group: A 1, A 2, B 1, B 2, E 1, E 2 E E 1+1 E 1-1 E 2+1 E 2-1 Additional labeling occurs for E symmetry species in order to distinguish between positive and negative K in a symmetric rotor basis set: E 1+1, E 1-1 and E 2+1, E 2-1 E2E2 E1E1 E 2+1 E 2-1 E 1+1 E 1-1 A2A2 A1A1 B2B2 B1B1 J, K a Selection rules: A 1 ↔ A 2 ; B 1 ↔ B 2 ; E 1 ↔ E 1 ; E 2 ↔ E 2 up to 10 transitions for each J and K a 13CH3NH2: 11 1 B B MHz 11 1 E E MHz 11 1 A A MHz 11 1 E E MHz 11 1 E E MHz 11 1 B B MHz 11 1 A A MHz 11 1 E E MHz 11 1 E E MHz 11 1 E E MHz

Lille sub-mm wave spectrometer Absorbing cell SR7270 DSP Lock-in amplifier InSb Bolometer Amplifier Synthesizer Agilent E8257D GHz Active sextupler 75 – 105 GHz//+15 dBm Ethernet hub x6 x2: 150 – 215 GHz x3: 225 – 315 GHz x5: 400 – 530 GHz x6: 500 – 630 GHz x9: 750 – 945 GHz x2: 150 – 215 GHz x3: 225 – 315 GHz x5: 400 – 530 GHz x6: 500 – 630 GHz x9: 750 – 945 GHz xNxN N = 2, 3, 5, 6(2x3), 9(3x3)

13 CH 3 NH 2 spectrum 775 – 945 GHz E 2-1 E 2+1 E 1+1 E 1-1 B 1, B 2 A 1, A 2 ΔJ=0, K=6←5

14 N nuclear quadrupole hyperfine structure Hyperfine splittings Fit f hf Rotational frequencies f rot Global fit Expectation values Hyperfine constants Torsional- Wagging- Rotational parameters Two-step fitting scheme: pure rotational transitions 1.Hyperfine splittings to get pure rotational transitions torsional- wagging-rotational parameters 2.Rotational transitions to get torsional- wagging-rotational parameters

Hyperfine structure: results 1878 hyperfine components were used to determine 970 rotational frequencies and 2 hyperfine constants rms = MHz wrms = CH 3 NH 2 12 CH 3 NH 2 χ + (MHz) (32) (12) χ – (MHz)6.0661(36)6.0646(24)

The Hamiltonian K, K’ K K’ 0 1 J 0 1 J off diagonal contributions for lKl=1 The Hamiltonian matrix n =1: nontunneling motion n = 2, 4, 6…: tunneling involving wagging n = 3, 5, 7…: tunneling involving torsion Ohashi and Hougen, J. Mol. Spec (1987) Ohashi et al., J. Mol. Spec (1988)

13 CH 3 NH 2 results as of 10/06/ rotational transitions in the range 150 – 950 GHz J max = 43, K a,max = fitted parameters rms = MHz wrms = CH 3 NH 2 12 CH 3 NH 2 A (MHz) (61) (11) B (MHz) (13) (32) C (MHz) (13) (32) wagging h 2v (MHz) (11) (77) h 4v (MHz)2.7313(10) (95) q2q (40) (52) f2f (66) (38) torsion h 3v (MHz) (15) (12) h 5v (MHz) (68) (55) f3f (14) (25) Dr. Ohashi’s code improved and extended to treat transitions with J>30

13 Acknowledgements Dr. N. Ohashi for providing his code for methylamine Programme National de Physico-Chimie du Milieu Interstellaire - CNRS ANR-08-BLAN-0054 Dr. N. Ohashi for providing his code for methylamine Programme National de Physico-Chimie du Milieu Interstellaire - CNRS ANR-08-BLAN-0054