We report on the dynamics of electronically excited o-, m-, and p-xylene on the femtosecond timescale by employing the vacuum-ultraviolet pump-IR probe mass spectrometry technique. The molecules were excited by the fifth harmonic (λ=160 nm) of a Ti:sapphire laser at a superposition of the S3 valence with several Rydberg states. The relaxation pathways were investigated by studying the parent P(+) and the fragment [P-H](+) and [P-CH3 ](+) time-resolved signals generated after interaction with the fundamental beam (λ=800 nm). Relaxation from the excited valence states was found to depend on the relative positions of the methyl groups on the ring. An increasing trend in the order o<m<p was observed for the lifetime of S3 , whereas that of the second valence state S2 presented the opposite trend. Conclusions on the possible deformations and vibrations induced during the relaxation process were drawn: ring deformation involving methyl motion takes place.
Keywords: femtochemistry; molecular dynamics; photochemistry; photophysics; xylenes.
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