MO STUDY OF THE BENZYLPEROXYL RADICAL, AN INTERMEDIATE IN ATMOSPHERICOZONE FORMATION

Unrestricted Hartree-Fock calculations have been carried out to study the benzylperoxyl radical, an intermediate atmospheric contaminant. Fo r this purpose, quantum mechanical MP2//UHF ab initio calculations wer e performed by using 6-31G* and 6-31+G** basis sets. Because no previ ous experimental nor theoretical data were available for benzylperoxyl , the results were compared with those of the smaller unsaturated pero xyl radicals, such as allylperoxyl. It is found that the calculated ab solute minimal energy corresponds to a trans conformation in which the O-O bond is sticking away from the benzene ring. Benzylperoxyl is fou nd also to exhibit an unusually O-O small bond order, which reflects t he weakness of the bond, i.e. its ability to react with NO forming NO2 and subsequently ozone. A peculiar MO diagram is obtained, with the u npaired MO deeply located in the ''doubly'' occupied MO space. This ef fect is also observed in allylperoxyl. Structural parameters, charges, spin densities and dipole moments are also reported.