Semiclassical Trajectory Studies of Reactive and Nonreactive Scattering of OH(A²Σ⁺) by H₂ Based on an Improved Full‐Dimensional Ab Initio Diabatic Potential Energy Matrix

Abstract

We present a new full-dimensional diabatic potential energy matrix (DPEM) for electronically nonadiabatic collisions of OH(A 2 Σ + ) with H 2 , and we calculate the probabilities of electronically adiabatic inelastic collisions, nonreactive quenching, and reactive quenching to form H 2 O + H. The DPEM was fitted using a many-body expansion with permutationally invariant polynomials in bond-order functions to represent the many-body part. The dynamics calculations were carried out with the fewestswitches with time uncertainty and stochastic decoherence (FSTU/SD) semiclassical trajectory method. We present results both for head-on collisions (impact parameter b equal to zero) and for a full range of impact parameters. The results are compared to experiment and to earlier FSTU/SD and quantum dynamics calculations with a previously published DPEM. The various theoretical results all agree that nonreactive quenching dominates reactive quenching, but there are quantitative differences between the two DPEMs and between the b = 0 results and the all-b results, especially for the probability of reactive quenching.

Velocity map images from surface-hopping; reactive scattering of OH (2Σ+) + H2 (1Σ+g)

“…2). This is in disagreement with the recent simulations, 8 which imply the opposite results. Its worth noting they used six times greater collisional energies.…”

“…1 is semi-quantitatively similar to that found by ref. 8, for both models. By integrating until the last bin containing quenching trajectories, the non-quenching channels represent at least 86% of the cross section.…”

“…The near co-linear C Nn geometries are favored as the dominant quenching channel agrees with previously reported results. 8,9 There is a long range (dipole-quadrapole) interaction at linear or perpendicular to H 2 orientations depending on the atom OH face. Quenching in FWW2 model strongly prefers Hfacing OH entrance channel which also dominates the mechanism leading the production of Hydrogen (Fig.…”

“…Understanding the impact of this process in the OH(S + ) lifetime is of importance. A complementary body of theoretical work has been also taken place, [5][6][7][8] given the rich experimental data available. Much of this work culminated in two analytic models by Truhlar et al 6 and Yarkony et al, 7 and have more recently been used to perform dynamic simulations with them (Guo et al 8,9 ) to estimate a number of observables.…”

“…In this communication we generate velocity map images (VMI) and H product distributions, previously omitted. 8,9 Velocity Map imagining is a mature and popular method for obtaining simultaneous angles and velocities (and a wealth of other implicit information) from scattering experiments. 10 The popularity of this method makes it a natural choice for computational scientist to simulate, to effectively communicate results with experimentalist.…”