Torsion-rotation-vibration effects in the ground and first excited states of methacrolein, a major atmospheric oxidation product of isoprene

摘要

Methacrolein is a major oxidation product of isoprene emitted in the troposphere. New spectroscopy information is provided with the aim to allow unambiguous identification of this complex molecule, characterized by a large amplitude motion associated with the methyl top. State-of-the-art millimeter-wave spectroscopy experiments coupled to quantum chemical calculations have been performed. For the most stable s-trans conformer of atmospheric interest, the torsional and rotational structures have been characterized for the ground state, the first excited methyl torsional state (nu(27)), and the first excited skeletal torsional state (nu(26)). The inverse sequence of A and E tunneling sub-states as well as anomalous A-E splittings observed for the rotational lines of v(26) = 1 state clearly indicates a coupling between methyl torsion and skeletal torsion. A comprehensive set of molecular parameters has been obtained. The far infrared spectrum of Durig et al. [Spectrochim. Acta, Part A 42, 89-103 (1986)] was reproduced, and a Fermi interaction between nu(25) and 2 nu(27) was evidenced. (C) 2016 AIP Publishing LLC.