Photodissociation Dynamics of 2-Bromopropane Using Velocity Map Imaging Technique

摘要

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 (~2P_(3/2)) and Br* (~2P_(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_3H_7 moiety than the channel leading to Br*. The anisotropy parameters of β (Br) were obtained to be between 0.68 and 1.49, and β (Br*) between 0.73 and 1.96, indicating that the Br* product originates from direct excitation of the ~3Q_0 state and the ~1Q_1 → ~3Q_0 nonadiabatic transition, and the Br product from direct excitation of the ~1Q_1 or ~3Q_1 state and the ~3Q_0 → ~1Q_1 nonadiabatic transition. The curve crossing probabilities were determined to be increase with the wavelength. As compared with the case of CH_3Br, the two heavier branched CH_3 groups significantly enhance the Br (~2P_(3/2)) production from nonadiabatic contribution. The curve crossing from the ~3Q_0 to the ~1Q_1 surface is much higher than that of the reverse from the ~1Q_1 to the ~3Q_0 surface, which may have resulted from the difference in shape between the potential energy surfaces of the ~3Q_0 and ~1Q_1 states. Finally, based on the experimental data, the partial absorption cross sections of the A band for the ~3Q_0, ~3Q_1, and ~1Q_1 states were extracted.