Vectorial Imaging of the Photodissociation of 2-Bromobutane Oriented via Hexapolar State Selection

TL;DR

This study employs vectorial imaging to analyze the correlation between molecular vectors during the photodissociation of oriented 2-bromobutane, revealing detailed angular relationships and transition characteristics in the dissociation process.

Contribution

It introduces a detailed vector correlation analysis in photodissociation of oriented asymmetric-top molecules, advancing understanding of molecular dynamics with orientation control.

Findings

Large anisotropy parameter of 1.85 for Br* fragment indicates a parallel transition.

Recoil angles are optimized to approximately 164°, showing specific vector correlations.

Photofragment angular distributions show minimal differences between enantiomers.

Abstract

Molecular orientation techniques are becoming available in the study of elementary chemical processes, in order to highlight those structural and dynamical properties that would be concealed by random rotational motions. Recently successful orientation was achieved for asymmetric-top and chiral molecules of much larger complexity than hitherto. In this work, we report and discuss the correlation between the vectors photofragment recoil velocity v, transition dipole moment {\mu}, and permanent dipole moment d in a dissociation experiment on hexapole oriented 2-bromobutane, photoinitiated by a linearly polarized laser. The sliced ion images of the Br* (2P1/2) and Br (2P3/2) photofragment were acquired at 234.0 and 254.1 nm, respectively, by (2+1) resonance-enhanced multiphoton ionization technique. A detailed analysis of the sliced ion images obtained at a tilting angle 45o of the laser polarization provides the information on correlation of the three vectors, which are confined by two polar angles {\alpha}, \c{hi} and one azimuthal angle {\phi}{\mu}d in the recoil frame. The sliced ion images of Br fragments eliminated individually from the enantiomers at 254.1 nm yield the asymmetric factor close to zero; for this reason the photofragment angular distributions do not show significant differences. The elimination of Br* fragment at 234.0 nm is mainly correlated with a parallel transition, giving rise to a large anisotropy parameter of 1.85, and thus can be considered as a single state excitation. The resulting recoil frame angles are optimized to 163.8{\deg} and 164.1{\deg} for {\alpha} and \c{hi}, respectively, whereas {\phi}{\mu}d approaches close to 0o for the best fit. Since in the present case, the three vectors have an only slight spatial arrangement, the photofragment angular distributions of the two enantiomers do not show appreciable differences...