Laser-induced fluorescence, dispersed fluorescence and lifetime measurements of jet-cooled chloro-substituted benzyl radicals

We measured the laser-induced fluorescence (LIF) and dispersed fluorescence (DF) spectra of jet-cooled α-, o- and m-chlorobenzyl radicals after they were generated by the 193 nm photolysis of the corresponding parent molecules. The vibronically resolved spectra were obtained to analyze their D1–D0 transitions. The fluorescence lifetimes of α-, o-, m- and p-chlorobenzyls in the zeroth vibrational levels of the D1 states were measured to estimate the oscillator strengths of a series of benzyl derivatives. It was found that the α-substitution is inefficient to break the `accidental forbiddennessʹ of the D1–D0 transition of benzyl, while the ring-substitution enhances the oscillator strength by 50%.