Ab initio study of excited electronic states and vibronic spectra of phenyl radical

Geometries, vibrational frequencies, excitation energies, and vibronic spectra of seven excited states of C ₆H ₅ have been studied by multireference ab initio calculations. For the 1 ²B ₁, 1 ²B ₂, 2 ²B ₂, and 2 ²B ₁ states the most intense vibronic peaks are calculated at 17952, 37744, 43380, and 43251 cm ^-1, respectively, and for 1 ²A ₂, 2 ²A ₁, and 3 ²A ₁ upper estimates for adiabatic excitation energies are 22176, 30988, and 42543 cm ^-1. We have assigned the 530-440 nm band in the absorption spectra to 1 ²B ₁ with possible contribution from 1 ²A ₂, the 265-230 nm band to 1 ²B ₂ and 3 ²A ₁, and intense peaks starting from ∼212 nm to 2 ²B ₁ and 2 ²B ₂.