Semiclassical Wigner theory of photodissociation in three dimensions: Shedding light on its basis

Abstract

The semiclassical Wigner theory (SCWT) of photodissociation dynamics, initially proposed by Brown and Heller [J. Chem. Phys. 75, 186 (1981)] in order to describe state distributions in the products of direct collinear photodissociations, was recently extended to realistic three-dimensional triatomic processes of the same type [Arbelo-González et al., Phys. Chem. Chem. Phys. 15, 9994 (2013)]. The resulting approach, which takes into account rotational motions in addition to vibrational and translational ones, was applied to a triatomic-like model of methyl iodide photodissociation and its predictions were found to be in nearly quantitative agreement with rigorous quantum results, but at a much lower computational cost, making thereby SCWT a potential tool for the study of polyatomic reaction dynamics. Here, we analyse the main reasons for this agreement by means of an elementary model of fragmentation explicitly dealing with the rotational motion only. We show that our formulation of SCWT makes it a semiclassical approximation to an approximate planar quantum treatment of the dynamics, both of sufficient quality for the whole treatment to be satisfying.

Femtochemistry under scrutiny: Clocking state-resolved channels in the photodissociation of CH3I in the A-band

“…The CH 3 I molecule is an ideal prototype to develop theoretical models to describe photodissociation processes [37,38]. In this work, the CH 3 I system is represented by considering four degrees of freedom (R, r, α, θ), where the dissociation coordinate R is the distance between I and the CH 3 center-of-mass, r is the symmetric C-H bond distance representing the CH 3 symmetric stretch mode (ν 1 mode), α is the umbrella bending angle of the CH 3 group (ν 2 mode), and θ is the in-plane H 3 -C-I bending angle (ν 6 mode) between the C-I axis and the axis perpendicular to the plane containing the three hydrogen atoms.…”

Photoelectron–Photofragment Coincidence Studies on the Dissociation Dynamics of the OH–CH4 Complex

“…To account for quantum effects, the initial conditions of the trajectories were selected based on the Wigner approach, initially suggested by Heller . This approach has been shown to provide a better description of initial conditions in photoexcited processes. , …”

Non-Resonant Probing of the Methyl Fragment at 213 nm following 266nm Photolysis of Methyl Iodide

“…The photodissociation of methyl iodide following excitation to A-band, which is a broad continuum ranging from 220 nm to 350 nm with a maximum around 260 nm is well studied both theoretically [20][21][22][23] and experimentally. 7,9,10,16,17 The A-band of methyl iodided is a σ*←n excitation from the lone pair on iodine to the lowest anti-bonding molecular orbital resulting in three broad, optically allowed transitions to dissociative states namely 1 Q1, 3 Q0 and 3 Q1.…”