Stereodynamics Imaging of Bromine Atomic Photofragments Eliminated from 1-Bromo-2-methylbutane Oriented via Hexapole State Selector

TL;DR

This study investigates the photofragmentation dynamics of bromine from 1-bromo-2-methylbutane using ion imaging and molecular orientation techniques, revealing detailed angular distributions and transition contributions.

Contribution

It introduces a combined approach of ion imaging and molecular orientation to analyze photofragment angular distributions and transition types in bromine photolysis.

Findings

Determined anisotropy parameters for Br* and Br states.

Measured molecular orientation efficiency of 0.15.

Observed wavelength-dependent changes in angular anisotropy.

Abstract

Both single-laser and two-laser experiments were conducted to look into the ion-imaging of Br*(2P1/2) and Br(2P3/2) photo-fragmented from 1-bromo-2-methylbutane in the range 232-240 nm via a detection scheme of (2+1) resonance-enhanced multiphoton ionization. The angular analysis of these photofragment distributions yields the anisotropy parameter beta = 1.88 +/- 0.06 for the Br* excited state which arises from a parallel transition, while beta = 0.63 +/- 0.09 for the Br ground state indicates the contribution from both a perpendicular transition and a non-adiabatic transition. When a hexapole coupled with an orienting field was implemented, the parent molecules are spatially oriented to yield an orientation efficiency |<cos theta>| of 0.15. Besides the chi angle between the recoil velocity v and the transition dipole moment mu, orienting molecules allows for the evaluation of the angle alpha between v and the permanent molecular dipole moment d. The angular analysis of Br* photofragment distribution yields chi to be 11.5 degrees and alpha in the range from 160 degrees to 180 degrees with weak dependency. In the two-laser experiments, the angular anisotropy of Br photofragment distribution was found to be smaller (0.38 +/- 0.10) when the photolysis wavelength was red-shifted to 240 nm, suggesting the increasing contributions from perpendicular transitions.