Adiabatic and diabatic dynamics in the photodissociation of CH2BrCl

Abstract

The photodissociation dynamics of chlorobromomethane (CBM) were investigated between 193 and 242 nm by resonance-enhanced multiphoton ionization (REMPI) with time-of-flight mass spectrometry (TOFMS). Translational energy distributions, anisotropy parameters, and Br:Br* branching ratios were determined at 193 and 235 nm to explore the non-adiabatic dynamics near the avoided crossing. Additional measurements were made at intermediate wavelengths to characterize the wavelength dependence of the Br and Br* anisotropy parameters. The non-adiabatic crossing probabilities calculated by applying a one-dimensional Landau–Zener model were relatively insensitive to the excitation wavelength, indicating that the avoided crossing between 3A′ and 4A′ potentials lies in the exit channel. Additionally, we have determined the partial absorption cross sections for the excited states that contribute to the ultraviolet absorption spectrum of CBM.