Theoretical Investigations of Rate Coefficients for H + O₃ and HO₂ + O Reactions on a Full-Dimensional Potential Energy Surface

Abstract

In this work, a machine learning method is used to construct a high-fidelity multichannel global reactive potential energy surface (PES) for the HO3 system from 21452 high-level ab initio calculations at the explicitly correlated multireference configuration interaction (MRCI-F12) level of theory. The permutation invariance of the PES with respect to the three identical oxygen atoms is enforced using permutation invariant polynomials (PIPs) in the input layer of a neural network (NN). This PIP-NN representation is highly faithful to the ab initio points, with a root-mean-square error of 0.20 kcal/mol. Using this PES, the kinetics of H + O3 → OH + O2 (R1) and HO2 + O → OH + O2 (R2) reactions were investigated using a quasi-classical trajectory method over a wide temperature range (200–2000 K). It was found that the calculated thermal rate coefficients of R1 and R2, exhibiting positive and negative temperature dependences, respectively, are in reasonably good agreement with most experimental measured values. These temperature dependences can be attributed to the presence and absence of an entrance channel potential barrier.

Neural Network Potential Energy Surfaces for Small Molecules and Reactions

“…As computing power and the availability of software have progressed, NN-based PES fitting methods have become increasingly popular and are widely used and continue to be improved in current literature. ,,− This is true also for machine learning methods in computational chemistry and physics in general. They have made it possible to tackle some outstanding problems in computational chemistry, ,, such as exchange-correlation − and kinetic energy ,,, functional development, solution of the Schrödinger equation, − and prediction of properties without solving the Schrödinger equation − that require even more powerful hardware and software resources than PES fitting, and in addition, manpower with interdisciplinary knowledge.…”

Insights into the Formation of Hydroxyl Radicals with Nonthermal Vibrational Excitation in the Meinel Airglow

“…The cis-and trans-HOOO wells are separated with a small barrier, and these features are not expected to impact the dynamics in a significant way, thanks to their low energies relative to the reactant asymptote. In the entrance channel, there is a transition state (TS), lying 0.86 kcal/mol above the reactant asymptote, 20 which was shown to control the kinetics, particularly on the temperature dependence of the rate coefficient. 22 As discussed below, it also plays a key role in determining the energy disposal in the reaction.…”

“…Based on the previously reported PIP-NN PES for the HO 3 system, 20 all the QCT calculations were performed using the VENUS program package. 29,30 An ensemble of 120 000 trajectories was computed at each of the six different translational temperatures, T = 150, 220, 298, 360, 480, and 640 K, for both the H + O 3 and D + O 3 reactions.…”

“…In this Letter, we report a detailed QCT dynamic study of the H/D + O 3 reactions on a highly accurate PES recently constructed from a large number of multireference configuration interaction (MRCI) points using the high-fidelity permutation invariant polynomial-neural network (PIP-NN) method. , The MRCI treatment of the PES is essential due to the multireference nature of this system. Indeed, this PES has been shown to reproduce accurately the reaction kinetics of the H + O 3 reaction .…”

“…Based on the previously reported PIP-NN PES for the HO 3 system, all the QCT calculations were performed using the VENUS program package. , An ensemble of 120 000 trajectories was computed at each of the six different translational temperatures, T = 150, 220, 298, 360, 480, and 640 K, for both the H + O 3 and D + O 3 reactions. After testing with a small set of trajectories, the maximal impact parameter b max was determined to be 3.0 Å for both reactions over the entire temperature range.…”