15min:

HOLGER S. P. MÜLLER, I. Physikalisches Institut, Universität zu Köln, 50937 Köln; B. J. DROUIN, J. C. PEARSON, L. R. BROWN, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA; I. KLEINER, LISA, Université Paris 12 & Paris 7 & CNRS, 94010 Créteil, France; R. L. SAMS, PNNL, Richland, WA 99352, USA.

Methyl cyanide, CH₃CN, is an important interstellar molecule, in particular in hot and dense molecular cores, and it may play a role in the atmospheres of planets or of Titan. Therefore, we have recorded extensive rotational and rovibrational spectra up to 1.6 THz and 1500 cm^-1, respectively. The present investigation extends our analysis of states with v₈ \leq 2 at vibrational energies below 740~cm^-1 and takes into consideration findings from an analysis of the ₄ band and the higher-lying ₇ (at 1042~cm^-1) and 3 ₈ ¹ (at 1078~cm^-1) bands. The rotational data extend to J = 87 and K = 15, infrared assignments currently extend to 55 and 12, respectively. Parameters affecting only v₇ = 1 or v₈ = 3 as well as some additional interaction parameters were kept fixed to values from (b). The largest perturbations of v₄ = 1 are caused by a k = 0, l = 3 interaction with v₈ = 3 at K = 8. Despite the inclusion of the interaction parameter and a centrifugal distortion correction, residuals amount to more than 200~MHz very close to the resonance. Removal of these residuals probably requires explicit inclusion of v₈ = 3 data. Several additional perturbations exist at lower as well as higher K with v₈ = 2, v₇ = 1 and v₈ = 3. Higher values of K are difficult to reproduce in spite of an extensive set of distortion parameters which, at highest orders, have rather large magnitudes, possibly indicating unaccounted interactions which would probably occur with states even higher than v₈ = 3.