Two-mode vibronic interaction between neighboring 1 2A2 and 2 2B2 excited electronic states of the benzyl radical

Publisher Website
Google Scholar
Abstract
The 2 2B2–1 2B2 transition of the benzyl radical occurs in the same frequency region as the 1 2A2–1 2B2 transition. Vibronic coupling between the 2 2B2 and 1 2A2 excited electronic states via 6b and 18b vibrational modes is shown to be responsible for the unusual structure of the electronic spectrum of benzyl observed in the visible region. Calculations of vibronic interaction were carried out using a model constructed with crude adiabatic, harmonic oscillator basis functions. The model was expressed in terms of four dimensionless parameters: D, the energy separation between the deperturbed 2 2B2 and 1 2A2 states; Cα and Cβ, which are interaction constants for the α≡18b and β≡6b modes, respectively; the ratio ωα/ωβ of these zero‐order mode frequencies. The possible range of these constants is discussed in detail. The model reproduces well the vibronic energies and relative transition intensities of bands observed within 700 cm−1 of the 1 2A2–1 2B2 transition origin for isotopic benzyl radicals. The deperturbed 2 2B2 state origin is found to lie between 430 and 485 cm−1 above the 1 2A2 state in gas phase benzyl‐h7 and between 355 and 370 cm−1 in benzyl‐d7.