The role of conical intersections in the nonadiabatic quenching of OH(A 2Σ+) by molecular hydrogen

Abstract

The role of the C 2v (1 2 B 2 -1 2 A 1 ), C s (1 2 AЈ -2 2 AЈ), and C ϱv (1 2 ⌸ -1 2 ⌺ ϩ ) seams of conical intersection in the dynamics of the nonadiabatic quenching of OH(A 2 ⌺ ϩ ) by molecular hydrogen is investigated. The locus of the C 2v and C ϱv conical intersections and the C s seam bridging them is determined. The accessibility of these seams following optical excitation from the ground 1 2 B 2 state of the OH-H 2 van der Waals complex is examined. Using linear interpolation pathways on the 2 2 AЈ potential-energy surface connecting these seams and the Franck-Condon region for vertical excitation as a guide, a transition state separating the 2 2 AЈ van der Waals complex from the seam of conical intersection was located. The barrier of 8.44 kcal mol Ϫ1 is due primarily to the required rotation of the OH molecule relative to H 2 . Finally, gradient descent paths from the conical intersection were determined to identify the possible products of the nonadiabatic quenching. For each seam, pathways leading to both OHϩH 2 and H 2 OϩH products were found.

A novel Gaussian Binning (1GB) analysis of vibrational state distributions in highly excited ${\rm H}_\text{2}$H2O from reactive quenching of OH* by ${\rm H}_\text{2}$H2

“…Theoretically, relevant work on this quenching has been done by Yarkony and co-workers, using multiconfigurational SCF and CI calculations to determine the conical intersections. [39][40][41] Limited two degree of freedom potential energy surfaces were also reported which qualitatively account for the high degree of rotational excitation of the quenched OH radical in the nonreactive channel. 42 Fu et al performed QCT calculations on the ground electronic state initiated from conical intersections with the lowest energy excited electronic state at the total energy of experiment.…”

An ab initio quasi-diabatic potential energy matrix for OH(2Σ) + H2

“…These reactions (and isotopic analogues) have generated substantial experimental interest in recent years. [8][9][10][11][12][13][14][15][16][17] Moreover, there has been significant theoretical interest in the electronic structure and conical intersections of this system, 10,18,19 and in the general question of adiabatic to diabatic transformations (ADTs) in molecules with conical intersections. [20][21][22][23][24] As a consequence, this system represents a benchmark test case for the development of theoretical reaction dynamics for polyatomic molecules in multiple electronic states.…”

Conical Intersections and the Spin‐Orbit Interaction

“…The molecular orbitals were constructed from a state-averaged multiconfigurational self-consistent field procedure [31] using an extended atomic orbital basis on oxygen and hydrogen. The details of this description can be found in [30].…”

“…The nonrelativistic 1,2 2 A 0 conical intersection seam in the H 2 þ OH supermolecule has been well studied [28][29][30] because of its role in the non-adiabatic quenching reaction Fig. 1).…”