1. Toward a global model of low-lying vibrational states of methyl cyanide, CH 3 CN: the v 4 = 1 state at 920 cm –1 and its interactions with nearby states Holger S. P. Müller, B. J. Drouin, J. C. Pearson, L. R. Brown, I. Kleiner, R. L. Sams 65th International Symposium on Molecular Spectroscopy; RC12

2. Motivation present in planetary atmospheres (Titan, Earth) − 5 isotopic species detected, incl. CH 2 DCN; 13 CH 3 13 CN + ?? − satellites of several vibrationally excited states detected − v 8 = 1 transitions detected for 13 C species − used as temperature probe (esp. hot cores) − considered to be a weed species important molecule in InterStellar Medium (ISM), especially hot cores, and in CircumStellar Envelopes (CSE)

3. Low-Lying Vibrational States of CH 3 CN v 8 = 4 v 8 = 3 v 8 = 2 v 8 = 1 v = 0 1200 800 400 0 E / cm −1 v 4 = 1 v4 = v8 = 1v4 = v8 = 1 v 7 = 1 v7 = v8 = 1v7 = v8 = 1 v 3 = 1 v 6 = 1

4. The ν 4 Band of CH 3 CN  ν 4 = ν(C–C), parallel band  favorable frequency region for remote sensing  weak band strengths: ν 4 4.8 cm –2 atm –1 ; ν 8 (4.4), 2ν 8 (6.2), ν 7 (11.7) ν 6 etc (94)

5. Previous and Present Work v = 0 for 6 isotopologs: H. S. P. Müller et al., A&A 506 (2009) 1487 v 8 ≤ 2: H. S. P. Müller et al., 62nd Ohio Symp, 2007, WG03 ν 4, ν 7, 3ν 8 : A. M. Tolonen et al., JMSp 160 (1993) 198 (parameters for v 7 = 1 and v 8 = 3 mostly from that study) v 4 = 1: J. Cosleou et al., JMSp 146 (1991) 49 + ref.; ≤ 460 GHz NEW: JPL & U Köln, ~ 310 lines, ≤ 1.439 THz, J max = 79, K max = 16; unc. ~50 kHz ν 4 : PNNL, p = 30 Pa, l = 19 m, res.: 0.00164 cm −1 ~ 1050 lines, J max = 56, K max = 12; current unc.: 0.1 mK intensities, broadening, and selected positions: C. P. Rinsland et al., JQSRT 109 (2008) 974

6. Rotational Spectrum of CH 3 CN at the Level of CH 3 C 15 N × 13 CH 3 CN, K = 10, 9 + CH 3 13 CN, K = 9, 8 ♥ CH 3 CN, v 8 = 1, k = –15, 17 ▼ CH 2 DCN, K = 9

7. 13 CH 3 13 CN: Intensity ≈ CH 3 CN @ 2000 cm –1

8. K Level Structure of v = 0 and v 8 = 1 400 0 800 1200 E / cm −1 5 10 15 v = 0 5 10 15 5 10 v 8 = 1 l = +1 l = −1 AζAζ q 22 14 12

9. Interactions between v 8 = 1 and v 8 = 2 Detail of the K Level Structure 15 l = +1 l = −1 15 v 8 = 1 1000 1250 1500 1750 E / cm −1 10 15 l = +2 10 l = 0 v 8 = 2 l = −2 10 14 11 13 15 13

10. Perturbations of v 4 = 1 by Nearby States v 8 = 3 v 8 = 2 v 4 = 1 v 7 = 1 +1 –1 +1 –1 –3 +2 +3 –2–2 0 = ΔK, Δl 0, 0 K > 20 3, 0 K = 5, 8; J = 57 1, –2 K = 5, 6; J = 73 0, 3 K = 8, J = 65, 66 –2, 1 K = 7, 5; J > 75 –1, –1 K > 20 –2, 1 K = 7, 5; J = 40, 41

11. Interaction of v 4 = 1, K = 5 with v 8 = 2, K = 8 0 @ J' = 57

12. The region of v 4 = 1, J = 63 – 62

13. Section of the Fortrat Diagram

14. Interaction Parameters (MHz) Involving v 4 = 1 Determined from a combined fit using SPFIT

15. Acknowledgements H.S.P.M. and the CDMS are supported by the Bundesminiterium für Bildung und Forschung (BMBF) administered through Deutsches Zentrum für Luft- und Raumfahrt (DLR; the German space agency). I.K. thanks the Programme National de Plane´tologie (PNP, France) for their funding of the project. Part of the research at the Jet Propulsion Laboratory (JPL), California Institute of Technology, was performed under contract with the National Aeronautics and Space Administration. Part of the experimental work was performed at the W.R. Wiley Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory. PNNL is operated for the United States Department of Energy by the Battelle Memorial Institute under Contract DE-AC05-76RLO 1830.