Electronic states of the phenoxyl radical

The phenoxyl radical and two of its isotopomers were investigated by UV-VIS and IR polarization spectroscopy of molecular samples immobilized in cryogenic argon matrices. Analysis of the combined electronic and infrared linear dichroism data led to determination of absolute transition moment directions and symmetry assignments for four low-lying excited electronic states. The bands observed at 16 000, 25 200, 33 900, and 41 800 cm−1 were assigned to A12, B12, A12, and B12 π–π* states, respectively. A very weak transition observed in the near-infrared close to 8900 cm−1 was assigned to an optically forbidden B22 n–π* state. The electronic transitions predicted by time dependent density functional theory (TD-UB3LYP/cc-pVTZ) were in good agreement with the observed transitions.