title: High-resolution infrared spectrum of jet-cooled methyl acetate in the C=O stretching region: internal rotations of two inequivalent methyl tops.
abstract: The jet-cooled high resolution infrared (IR) spectrum of methyl acetate (MA), CH(3)-C(=O)-O-CH(3), in the C=O fundamental band region was recorded by using a rapid scan IR laser spectrometer equipped with an astigmatic multipass cell. No high resolution IR analyses of the ro-vibrational transitions between the ground and non-torsionally excited vibrational states have hitherto been reported for molecules with two inequivalent methyl rotors. Because of the two chemically different methyl tops in MA, i.e., the acetyl -CH(3) and methoxy -CH(3), each rotational energy level is split into more than two torsional sublevels by internal rotations of these methyl groups. We were able to assign ro-vibrational transitions of four torsional species by using the ground state combination differences calculated from the molecular constants of the vibrational ground state recently determined by a global fit of the microwave and millimeter wave lines [M. Tudorie, I. Kleiner, J. T. Hougen, S. Melandri, L. W. Sutikdja, and W. Stahl, J. Mol. Spectrosc. 269, 211 (2011)]. The assigned lines were successfully fitted using the BELGI-Cs-IR program to an overall standard deviation which is comparable to the measurement accuracy. This study is also of interest in understanding the role of methyl rotors in the intramolecular vibrational-energy redistribution processes in mid-size organic molecules.
authors.affiliation: Department of Chemistry, University of Alberta, Edmonton, Alberta T6G 2G2, Canada.
authors.forename: Fumie X
authors.initials: FX
authors.lastname: Sunahori
authors.forename: Nicole
authors.initials: N
authors.lastname: Borho
authors.forename: Xunchen
authors.initials: X
authors.lastname: Liu
authors.forename: Yunjie
authors.initials: Y
authors.lastname: Xu