The dynamics of excited states in o-xylene molecules has been studied by femtosecond time-resolved photoelectron imaging coupled with time-resolved mass spectroscopy. The ultrafast internal conversion from the S(2) state to the vibrationally hot S(1) state on timescale of 60 fs is observed on real time. The secondarily populated high vibronic S(1) state deactivates further to the S(0) state on timescale of 9.85 ps. Interestingly, the lifetime of the low vibronic S(1) state is much longer, extrapolated to ~12.7 ns. The great differences of lifetime of different vibronic S(1) state are due to their different radiationless dynamics.

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Photodissociation dynamics of 2-bromopropane in the A band was investigated at several wavelengths between 232 and 267 nm using resonance-enhanced multiphoton ionization technique combined with velocity map ion-imaging detection. The ion images of Br ((2)P(3/2)) and Br* ((2)P(1/2)) were analyzed to yield corresponding total translational energy and angular distributions. The total translational energy distributions showed that the channel leading to Br carried more internal energy in the 2-C(3)H(7) moiety than the channel leading to Br*. The anisotropy parameters of beta (Br) were obtained to be between 0.68 and 1.49, and beta (Br*) between 0.73 and 1.96, indicating that the Br* product originates from direct excitation of the (3)Q(0) state and the (1)Q(1) --> (3)Q(0) nonadiabatic transition, and the Br product from direct excitation of the (1)Q(1) or (3)Q(1) state and the (3)Q(0) --> (1)Q(1) nonadiabatic transition. The curve crossing probabilities were determined to be increase with the wavelength. As compared with the case of CH(3)Br, the two heavier branched CH(3) groups significantly enhance the Br ((2)P(3/2)) production from nonadiabatic contribution. The curve crossing from the (3)Q(0) to the (1)Q(1) surface is much higher than that of the reverse from the (1)Q(1) to the (3)Q(0) surface, which may have resulted from the difference in shape between the potential energy surfaces of the (3)Q(0) and (1)Q(1) states. Finally, based on the experimental data, the partial absorption cross sections of the A band for the (3)Q(0), (3)Q(1), and (1)Q(1) states were extracted.