Chemical Physics Letters, Vol.363, No.5-6, 435-440, 2002
Nuclear coordinate dependence of electronic transition moments involving torsional modes: the Franck-Condon/symmetry forbidden m(0)(3+) band in the allowed S-1 <- S-0 transition of toluene
A novel theory of vibronic intensity borrowing by large-amplitude vibrations was developed in a form to modify the conventional Herzberg-Teller theory. The ingredients are: (1) Crude Born-Oppenheimer wavefuntions (CBO Wf's) at more-than-one (2 x 2 x 3 = 12) conformations were used as building blocks of the adiabatic BO Wf. (2) The latter was made to belong to the molecular symmetry group (G(12)) by Fourier-series expansion terminated at the low (ninth) order. (3) The non-Born-Oppenheimer effect was shown to be less significant. The experimental observation of the subtitle was successfully interpreted with this formalism, endorsing the previous assertion by Walker et al. (C) 2002 Elsevier Science B.V. All rights reserved.