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 sh own that, for a correct description of the radical structures, both an appropriate treatment of electron correlation and polarization functi ons in the basis set are extraordinarily important. Calculations at th e highest level indicate that the CO bond length in these radicals is close to that of p-benzoquinone, and the ring skeletons adopt a quinoi d structure. The ab initio force fields calculated at the UNO-CAS leve l reproduced the prominent spectral features of these radicals satisfa ctorily. On the basis of the ab initio calculations, the strongest res onance Raman band observed at about 1510 cm-1 is reassigned to the C=C stretching vibration.