Vibronic relaxation pathway in methyl-substituted benzyl radicals

We report a new evidence of vibronic relaxation pathway in methyl-substituted benzyl radicals from the analysis of the origin bands of the vibronic emission spectra observed. The jet-cooled methyl-substituted benzyl radicals generated in a corona discharge experience stepwise vibrational relaxation to the vibrationless state within their own electronic states, from which the crossing from the D2 to D1 states is possible through vibronic coupling using the vibrational modes in the D1 state. Thus, it has been turned out that the energy difference between the D2 and the D1 states is an important factor in determining the efficiency of vibronic coupling.