Torsion-vibration coupling in S1 toluene: Implications for IVR, the torsional barrier height, and rotational constants

Jason Gascooke, Edwina Virgo, Warren Lawrance

    Research output: Contribution to journalArticle

    Abstract

    We have examined the S1←S0 transition of toluene in the region from the 0 0 0 band to ∼210 cm-1 above it. The spectrum reveals methyl rotor levels of 00 toluene up to m = 6 and of the lowest frequency vibration, 201, up to m = 4. The rotor levels of both 201 and 00 are perturbed by torsion-vibration coupling. The inclusion of torsion-vibration coupling leads to the S1 torsional barrier, V6, being revised from -26.376 cm-1 to -5.59 cm-1. The torsion-vibration coupling constant is determined to be 21.1 cm-1. This situation is the S1 analogue of that recently reported for S0 toluene [Gascooke et al., J. Chem. Phys. 142, 024315 (2015)]. Torsion-vibration coupling alters both the rotor band positions and the rotational contours, which particularly affects the rotational constants associated with motion around the a-axis, about which the methyl group rotates. Every vibrational state (indicated generically by X) will be involved in the corresponding X - X201 torsion-vibration coupling; so, this interaction permeates the vib-rotor manifold, providing a mechanism to enhance intramolecular vibrational energy redistribution.

    Original languageEnglish
    Article number044313
    JournalJournal of Chemical Physics
    Volume143
    Issue number044313
    DOIs
    Publication statusPublished - 2015

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