Swinn AK, Kable SH
School of Chemistry, University of Sydney, Sydney, NSW, 2006, Australia
J Mol Spectrosc. 1998 Sep;191(1):49-67. doi: 10.1006/jmsp.1998.7608.
A detailed study of the S1(1A1)-S0(1A1) transition of jet-cooled o-difluorobenzene has been completed using the two techniques of laser-induced fluorescence excitation and dispersed, single vibronic level fluorescence spectroscopy. Analysis of over 60 dispersed fluorescence spectra resulted in both the assignment of 22 excited state vibrational frequencies and the confirmation of 23 ground state frequencies. The spectrum is dominated by Franck-Condon activity in totally symmetric vibrations with long progressions in the ring-breathing mode, nu9. By analogy with benzene and the para- and meta-substituted isomers, two vibronic coupling mechanisms are postulated to be responsible for the wealth of weaker symmetry-forbidden structure that has been observed. Single quantum changes in b2 vibrations are postulated to appear due to first order vibronic coupling to a higher lying B2 electronic state. Combinations of b1 and a2 modes are postulated to appear from second order vibronic coupling to an A1 electronic state. This second order coupling causes a pronounced Duschinsky mixing among excited state b1 and a2 modes with respect to their ground state counterparts. Franck-Condon factors are calculated for the a1 progression-forming modes, anharmonic contributions are evaluated, one strong Fermi resonance is identified and analyzed, and the Duschinsky rotation matrix elements are evaluated for the most strongly affected modes, nu17 and nu18. Several transitions in the oDFB-oDFB van der Waals dimer and oDFB-Ar complex are also assigned in the spectrum. Copyright 1998 Academic Press.
利用激光诱导荧光激发和色散单振动能级荧光光谱这两种技术，完成了对喷射冷却邻二氟苯S1(1A1)-S0(1A1)跃迁的详细研究。对60多个色散荧光光谱的分析，既确定了22个激发态振动频率，又证实了23个基态频率。该光谱主要由全对称振动中的弗兰克-康登活性主导，在环呼吸模式ν9中有长进展。通过与苯以及对位和间位取代异构体类比，推测有两种振动耦合机制导致了所观察到的大量较弱的对称性禁戒结构。由于与较高的B2电子态的一级振动耦合，推测b2振动中会出现单量子变化。推测b1和a2模式的组合是由与A1电子态的二级振动耦合产生的。这种二级耦合导致激发态b1和a2模式相对于其基态对应模式发生明显的杜什insky混合。计算了形成a1进展的模式的弗兰克-康登因子，评估了非谐贡献，识别并分析了一个强费米共振，并对受影响最大的模式ν17和ν18评估了杜什insky旋转矩阵元。光谱中还确定了邻二氟苯-邻二氟苯范德华二聚体和邻二氟苯-氩络合物中的几个跃迁。版权所有1998年学术出版社。
