QUANTUM CHEMICAL AND VIBRONIC ANALYSIS OF THE 1 2B2REVERSIBLE12A2, 2(2B2) TRANSITION IN BENZYL-H7 AND BENZYL-D7 RADICALS

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 2B 2 transition in benzyl-h7 and benzyl-d7 radicals, arising from the activity of a1 and b1 in-plane modes. It is shown that the 6a01 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 2A 2 and 2 2B2 states are strongly mixed by v 8b and v6b modes. The unperturbed 1 2A 2 state lies ∼850 cm-1 below the unperturbed 2 2B2 state. The coupling depresses strongly the position of the 6b01 level mixing it markedly with the level arising from C-CH2 rock (v18b 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 v14 (b1) mode in the 1 2B 2 state is shown to be depressed markedly by vibronically induced mode mixing with v8b mode due to the 1 2B2-n 2A2 interactions. © 1990 American Institute of Physics.