Dynamics of Br(²P_j) Formation in the Photodissociation of Bromobenzene

Abstract

The photodissociation dynamics of bromobenzene near 234 nm has been investigated using a two-dimensional photofragment ion-imaging technique coupled with a state-selective [2+1] resonance-enhanced multiphoton ionization (REMPI) scheme. The nascent Br atoms are produced by the primary C-Br bond dissociation, which leads to the formation of C6H5 ( X % ) and Br( 2 Pj, j = 1/2, 3/2). The observed translational energy distributions have been fitted by a single Boltzmann function and two Gaussian functions. Trimodal translational energy distributions of Br( 2 Pj) have been assigned to the direct/indirect dissociation mechanisms originating from the initially excited 3 (π,π*) state. The assignments have been confirmed by the recoil anisotropy and distribution width corresponding to the individual components.

UV photolysis of 4-iodo-, 4-bromo-, and 4-chlorophenol: Competition between C–Y (Y = halogen) and O–H bond fission

“…Analysis of the Br image suggested a bimodal TKER distribution with an associated β = −0.02 ± 0.01, dominated by a slow, statistical component, while the yield of Br * products appeared to be negligible. Ground state Br atoms are also dominant in the 234 nm photolysis of PhBr, 33 but most of these products appear with substantial kinetic energy (with a mean TKER corresponding to ∼60% of E avl ) and positive recoil anisotropy.…”

Photodissociation Dynamics of C6F5Br at 234 nm: Fluorination Effects on Br/Br*Formation Pathways

“…In the short wavelength, significant UV absorption of bromobenzene is caused by and transition; the mixing between these states becomes more probable and additional routes can be observed as in the case of photodissociation of iodobezene. 8,14 With the purpose of elucidation of dissociation dynamics of bromobenzene at short-wavelengths, we have previously investigated 234 nm dissociation dynamics of bromobenzene using velocity ion map imaging.…”

“…In the short wavelength, significant UV absorption of bromobenzene is caused by and transition; the mixing between these states becomes more probable and additional routes can be observed as in the case of photodissociation of iodobezene. 8,14 With the purpose of elucidation of dissociation dynamics of bromobenzene at short-wavelengths, we have previously investigated 234 nm dissociation dynamics of bromobenzene using velocity ion map imaging.14 Observed trimodal translational distributions for Br/Br * formation channels have been attributed to the direct and indirect dissociation mechanisms originating from the initially excited (π, π * ) state. This is indicative that dissociation mechanisms of bromobenzene at 234 nm are more complicated than those near 270 nm.…”

“…It has been unraveled by numerous studies that dissociation pathways are substantially dependent on the type of halogen, 9-11 atomic substituents, 12 and excitation wavelengths. 13 In the early work on the bromobenzene (C 6 H 5 Br) photodissociation near 266 nm, [7][8][9][10][11][12]14 the main dissociation channel is an indirect dissociation involving the bound (π, π * ) and repulsive (π, σ * ) states. In the short wavelength, significant UV absorption of bromobenzene is caused by and transition; the mixing between these states becomes more probable and additional routes can be observed as in the case of photodissociation of iodobezene.…”

“…The A-band of alkyl bromide arises from the C-Br bond localized transition and consists of three overlapping transitions to repulsive states ( Q 1 PESs via a conical intersection along the C-Br bond coordinate. [4][5][6] Compared to the photodissociation of alkyl bromide, the photodissociation dynamics of aryl halides [7][8][9][10][11][12][13][14][15][16] show more complicated because more electronic states are involved and thus making multiple dissociation pathways probable. Multiple dissociation pathways include the predissociation between excited electronic states, internal conversion processes from vibrational excited states, and dissociation processes from repulsive states.…”