Imaging the alignment angular distribution: State symmetries, coherence effects, and nonadiabatic interactions in photodissociation

Abstract

We establish a rigorous theoretical connection between measurements of the angular distribution of atomic photofragment alignment and the underlying dynamics of molecular photodissociation. We derive laboratory and molecular-frame angular momentum state multipoles as a function of photofragment recoil angles. These state multipoles are expressed in terms of alignment anisotropy parameters, which provide information on state symmetries, coherence effects, and nonadiabatic interactions. The method is intended for analysis of experimental data obtained with two-photon spectroscopy and ion imaging techniques, although it is readily modified for treating Doppler or time-of-flight mass spectrometer peak profiles. We have applied this method to the photodissociation of Cl2 at 355 nm, where we observe strong alignment in the ground state chlorine atom photofragments. Our analysis demonstrates that there are important contributions to the alignment from both incoherent and coherent perpendicular excitation. We also show that the existence of atomic alignment due to coherence requires that nonadiabatic transitions occur at long range.

O(3PJ) Alignment from the Photodissociation of SO2 at 193 nm

“…geometries used, the appropriate expressions for the images are 20,27 where P 2 /P 0 is the line-strength factor for the probe (2 + 1)…”

Polarization of molecular angular momentum in the chemical reactions Li + HF and F + HD

“…98 A general method for extraction of orientation and alignment information from 2 + 1 REMPI measurements has been developed by Kummel and co-workers. 99, 100 A modification of this method that adapts it to the case of atoms and provides complete separation between the scalar and tensor quantities has been suggested by Bracker et al 101 However, both methods result in rather cumbersome expressions.…”

Determination of all scattering phases and amplitudes in the photodissociation of a diatomic molecule

“…Several experimental studies have reported measurements of such orientation and alignment parameters (generically referred to hereafter as anisotropy parameters) for photodissociation of a variety of diatomic systems (see, for example, [6][7][8][9][10][11][12][13][14][15][16]), and results have been used to infer certain non-adiabatic crossing probabilities and phase shifts [10], as well as the shapes of molecular potential energy curves [17]. Theoretical analysis by Balint-Kurti and coworkers [2,3] pointed the way to the determination of all amplitudes and phases of T-matrix elements, and illustrated the connection to anisotropy parameters by using wavepacket propagation to compute the photodissociation dynamics of HF and HCl.…”