THEORETICAL-STUDY OF THE STRUCTURE AND VIBRATIONS OF P-FLUOROPHENOXY AND P-CHLOROPHENOXY RADICALS - A NEW INTERPRETATION OF THE RESONANCE RAMAN-SPECTRA

Ab initio calculations at the ROHF and UNO-CAS levels were carried out on the structures of p-fluoro- and p-chlorophenoxy radicals. It is shown that, for a correct description of the radical structures, both an appropriate treatment of electron correlation and polarization functions in the basis set are extraordinarily important. Calculations at the highest level indicate that the CO bond length in these radicals is close to that of p-benzoquinone, and the ring skeletons adopt a quinoid structure. The ab initio force fields calculated at the UNO-CAS level reproduced the prominent spectral features of these radicals satisfactorily. On the basis of the ab initio calculations, the strongest resonance Raman band observed at about 1510 cm-1 is reassigned to the C=C stretching vibration.