AUTHOR=Jasper Ahren W. , Moberg Daniel R. , Tao Yujie , Klippenstein Stephen J. , Sivaramakrishnan Raghu 

TITLE=Inefficient intramolecular vibrational energy redistribution for the H + HO2 reaction and negative internal energy dependence for its rate constant

JOURNAL=Frontiers in Physics

VOLUME=10

YEAR=2022

URL=https://www.frontiersin.org/journals/physics/articles/10.3389/fphy.2022.1003010

DOI=10.3389/fphy.2022.1003010

ISSN=2296-424X

ABSTRACT=<p>Quasiclassical trajectories (QCT) and newly constructed global potential energy surfaces are used to compute thermal and nonthermal rate constants for the H + HO<sub>2</sub> reaction. The thermal QCTs rate constants are up to 50% smaller than transition state theory (TST) rate constants based on the same level of electronic structure theory. This reduction is demonstrated to result from inefficient intramolecular vibrational energy redistribution (IVR) in the transient H<sub>2</sub>O<sub>2</sub> well, with a significant fraction of trajectories that reach the H<sub>2</sub>O<sub>2</sub> well promptly dissociating back to reactants instead of <italic>via</italic> the heavily statistically favored 2OH channel. The nonstatistical reduction factor, <italic>κ</italic><sub>IVR</sub>, that quantifies this effect is shown to increase in importance with temperature, with <italic>κ</italic><sub>IVR</sub> = 0.81 at 300 K and 0.47 at 2500 K. Finally, we show that inefficient IVR causes H + HO<sub>2</sub> rate constants mediated by H<sub>2</sub>O<sub>2</sub> to depend inversely on the initial vibrational excitation of HO<sub>2</sub>.</p>