15min:

CAROLYN S. BRAUER, JOHN C. PEARSON, BRIAN J. DROUIN, SHANSHAN YU, JET PROPULSION LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY, 4800 OAK GROVE DR., PASADENA, CA 91109.

Propionitrile (CH₃CH₂CN) is observed with large column densities in a number of high-mass star-forming cores, where core temperatures exceed 200 K. It is a near-prolate ( =0.96) asymmetric top with appreciable dipole moment components on both the a- and b-axes (µ_a = 3.84 D, µ_b = 1.23 D). This, combined with the presence of four fundamental modes as well as four overtones and combination bands all occurring below 600 cm^-1, results in a very rich spectrum. It is known to be a major contributor to spectral line confusion in ground-based observations and is expected to complicate observations by Herschel, SOFIA and ALMA, making it imperative to fully characterize the entire spectrum. The lowest in-plane bend, ₁₃, is 206.9(0.5) cm^-1, and the first excited torsional state, ₂₁, which is just 186 GHz above, have been detected in hot cores with antenna temperatures of a few Kelvin. The close proximity of ₁₃ and ₂₁, as well as their low-lying nature, offers a unique opportunity to study the vibration-torsion-rotation coupling problem in the case of two nearly degenerate vibrational states. As expected from C_s symmetry and their A' and A'' nature, these states exhibit strong a- and b-symmetry Coriolis interactions, as well as interactions resulting from different sets of Eckhart-Sayvetz conditions being required in ₁₃ and ₂₁. In the present work, the ₁₃ and ₂₁ states of propionitrile have been analyzed to high frequency and angular momentum quantum number. The spectrum, molecular constants,and insights into the vibration-torsion-rotation problem will be discussed.