Br (2Pj) atom formation dynamics in ultraviolet photodissociation of tert-butyl bromide and iso-butyl bromide

Abstract

The photodissociation dynamics of tert- C4 H9 Br and iso- C4 H9 Br has been studied at 234 and 265 nm using two-dimensional velocity map imaging technique. The translational energy and angular distributions have been analyzed for Br, Br*, and tert- C4 H9 radical. The energy distribution of Br atom in the photodissociation of tert- C4 H9 Br is found to consist of two Gaussian components. The two components are correlated to two independent reaction paths on the excited potential energy surfaces: (1) the high-energy component from the prompt dissociation along the C-Br stretching mode and (2) the low-energy component from the repulsive mode along the C-Br stretching, coupled with some bending motions. For the energy distribution of Br* atom in the photodissociation of tert- C4 H9 Br, a third multiphoton dissociative ionization channel is observed at 265 nm in addition to the two energy components corresponding to channels (1) and (2). The energy distributions of Br and Br* atoms in the photodissociation of iso- C4 H9 Br can be fitted using only one Gaussian function indicating a single formation channel. Relative quantum yields for Br (P 32 2) at 234 and 265 nm in the photodissociation of tert- C4 H9 Br are measured to be 0.76 and 0.65, respectively. For iso- C4 H9 Br, the measured value is 234 nm (Br) =0.81. The contribution of bending modes to Br and Br* is much more obvious in the photodissociation of tert- C4 H9 Br than in iso- C4 H9 Br. © 2006 American Institute of Physics.