A THEORETICAL-STUDY ON THE ELECTRONIC AND VIBRATIONAL STRUCTURE OF THE PHENOXYL RADICAL

The electronic structures of the phenoxyl radical in the electronic ground and excited states are studied by ab initio MO calculations. The geometries are optimized by the CAS-MCSCF procedure with the Huzinaga-Dunning DZV basis set. The electronic excitation energies and transition dipole moments are calculated by the CI procedure. According to the result of the calculation the observed absorption bands at about 600, 400, and 300 nm are assigned as XB-2(1) --> 1B-2(2) (n --> pi), XB-2(1) --> 1(2)A2 and 2B-2(1) (pi --> pi*), and XB-2(1) --> 2(2)A2, respectively. In order to analyze the vibrational character of the absorption band at about 400 nm the force constants, the potential energy distributions, the normal modes, and the Franck-Condon integrals are calculated for the three states, XB-2(1), 1(2)A2, 2B-2(1). The force constants are scaled by referring to the experimental resonance Raman, Trapped Ion Photodissociation (TIP), and the matrix-isolated electronic absorption spectra. The strongest vibrational band of the TIP and the absorption spectra is assigned to the 0-0 band of the X --> 1(2)A2 transition and the second strongest, at a higher energy of 1110 cm-1, to the 0-0 band of the X --> 2B-2(1) transition. The theoretical vibronic absorption and Raman spectra are reproduced and compared favorably with the experimental spectra.