3,4-dimethylbenzyl radical formed in a corona discharge of 1,2,4-trimethylbenzene.

A precursor, 1,2,4-trimethylbenzene, seeded in a large amount of an inert carrier gas, helium, was electrically discharged in a corona-excited supersonic expansion using a pinhole-type glass nozzle. The blue-green colored fluorescence emanating from the downstream jet was recorded with a long path monochromator to observe the vibronic emission spectrum of the benzyl-type radical formed. Analysis of the spectrum suggests that the most dominant product of the corona discharge is the 3,4-dimethylbenzyl radical formed by extracting a hydrogen atom from the methyl group at the 4-position. The electronic energies of the D 1 and D 2 states and the vibrational mode frequencies of the 3,4-dimethylbenzyl radical were accurately obtained for the first time by comparison with those from an ab initio calculation as well as those of the known vibrational mode frequencies of the precursor.