American Institute of Physics, The Journal of Chemical Physics, 1(93), p. 600-608, 1990
DOI: 10.1063/1.459507
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The QCFF/PI+CI method and the CNDO/S+CI method in the floating atomic orbital basis set are used to study vibronic structure of the 1 2B2↔1 2A2, 2 2B2 transition in benzyl-h7 and benzyl-d7 radicals, arising from the activity of a1 and b1 in-plane modes. It is shown that the 6a10 line has its intensity almost entirely due to the borrowing from the 1 2A2↠1 2A2 transition via the 1 2A2–1 2A2 coupling. We demonstrate tha the 1 2A2 and 2 2B2 states are strongly mixed by ν8b and ν6b modes. The unperturbed 1 2A2 state lies ∼850 cm−1 below the unperturbed 2 2B2 state. The coupling depresses strongly the position of the 6b10 level mixing it markedly with the level arising from C–CH2 rock (ν18b in other assignments) fundamental. Three-mode vibronic analysis of the absorption and emission spectrum produces vibronic structure that agrees well with the observed spectra. The adiabatic frequency of the ν14 (b1) mode in the 1 2B2 state is shown to be depressed markedly by vibronically induced mode mixing with ν8b mode due to the 1 2B2–n 2A2 interactions.