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Torsional symmetry dependence of S 1 dynamics in molecules that undergo methyl internal rotation
Author(s) -
Moule David C.,
Judge Richard H.,
Liu Haisheng,
Lim Edward C.
Publication year - 1999
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/(sici)1097-461x(1999)71:2<167::aid-qua5>3.0.co;2-1
Subject(s) - chemistry , singlet state , symmetry (geometry) , relaxation (psychology) , excited state , excitation , acetaldehyde , context (archaeology) , molecule , internal rotation , atomic physics , rotation (mathematics) , spectral line , coupling (piping) , molecular physics , physics , quantum mechanics , materials science , mechanical engineering , geometry , mathematics , engineering , psychology , social psychology , paleontology , organic chemistry , ethanol , metallurgy , biology
The single‐rovibronic‐level fluorescence of “intermediate‐case” molecules that undergo methyl internal rotation is strongly influenced by the torsional symmetry of the lowest excited singlet state ( S 1 ). The most dramatic example of such symmetry dependence comes from our recent finding that the intensities of the e – e transitions in the high‐resolution S 1 ← S 0 fluorescence excitation spectra of jet‐cooled 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. ©1999 John Wiley & Sons, Inc. Int J Quant Chem 71: 167–176, 1999