Atmospheric temperatures and pressures cover such wide ranges that it is challenging to compute ab initio atmospheric rate constants from first principles. Recently, it was shown for several reactions that Semi-Classical Transition State Theory (SCTST) in partnership with high-level quantum chemistry can predict ab initio rate constants that are as accurate as experimental data. SCTST with ab initio quantum chemistry can also be used to compute the microcanonical rate constants (k(E)s) that are essential for master equation modeling of pressure-dependent reactions. In this paper, we describe state of the art master equation simulations of the important atmospheric reaction HO + CO (+M) ? HOCO ? H + CO2 for the full range of atmospheric temperatures and pressures. We discuss a deficiency we recently discovered in our previous model, and show how it can be circumvented, thus allowing predictions of product branching ratios even at low atmospheric temperatures. As in previous work using SCTST, the predicted total rate constants are in excellent agreement with measurements.

Atmospheric rate constants for HO + CO (+M) ? HOCO ? H + CO<sub>2</sub> from semiclassical transition state theory and ab initio quantum chemistry

248th National Meeting (2014)

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Atmospheric rate constants for HO + CO (+M) ? HOCO ? H + CO2 from semiclassical transition state theory and ab initio quantum chemistry

Atmospheric rate constants for HO + CO (+M) ? HOCO ? H + CO₂ from semiclassical transition state theory and ab initio quantum chemistry