Abstract
We report a two dimensional, laser induced fluorescence study of the lowest 345 cm-1 region of S 0 toluene. Methyl rotor levels of 0 0 up to m = 6 and of 20 1 up to m = 4 are observed. The rotor levels of 0 0 and 20 1 have quite different energy spacings that are well fit by a model that includes strong torsion-vibration coupling between them. The model requires that the rotor barrier height be revised from -4.84 cm-1 (methyl hydrogens in a staggered conformation) to +1.57 cm-1 (eclipsed conformation). However, the 3a 2 ″ state lies below the 3a 1 ″ state as expected for a staggered conformation due to energy shifts associated with the torsion-vibration coupling. It is shown that the rotor wave-functions exhibit little localization at the torsional energy minima. The variation in the m = 0 wavefunction probability distribution with torsional angle is shown to be very similar for the previously accepted negative V 6 value and the torsion-vibration coupling model as this coupling shifts the phase of the wavefunction by 30° compared with its phase for V 6 alone. The presence of a strong Δυ = ± 1 torsion-vibration coupling involving the lowest frequency vibrational mode provides a potential pathway for rapid intramolecular vibrational energy redistribution at higher energies.
Original language | English |
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Article number | 024315 |
Pages (from-to) | Article: 024315 |
Number of pages | 13 |
Journal | Journal of Chemical Physics |
Volume | 142 |
Issue number | 2 |
DOIs | |
Publication status | Published - 14 Jan 2015 |