Torsional symmetry dependence of S1 dynamics in molecules that undergo methyl internal rotation
✍ Scribed by David C. Moule; Richard H. Judge; Haisheng Liu; Edward C. Lim
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 391 KB
- Volume
- 71
- Category
- Article
- ISSN
- 0020-7608
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✦ Synopsis
The single-rovibronic-level fluorescence of ''intermediate-case'' molecules that undergo methyl internal rotation is strongly influenced by the torsional Ž . symmetry of the lowest excited singlet state S . The most dramatic example of such 1 symmetry dependence comes from our recent finding that the intensities of the e᎐e transitions in the high-resolution S ¤ S fluorescence excitation spectra of jet-cooled 1 0 acetaldehyde become very weak relative to the a᎐a transitions at higher beam temperatures. In this study, we rationalize this remarkable torsional symmetry dependence of electronic relaxation in acetaldehyde on the basis of internal-overall rotation coupling that leads to symmetry-selective increase in the density of states for singlet-triplet coupling. Related observations by others on aliphatic carbonyls and diazabenzenes are also discussed within the context of the coupling between the internal and overall rotation.