Quantum chemical calculations at QCISD and CCSD­(T) levels of theory have been performed to investigate the effect of NH3 and HCO2H on the reaction between OH• and HCl. Potential energy profiles indicate that both NH3 and HCO2H catalyzed reactions could proceed through two different channels, namely, single and double hydrogen atom transfer. Theoretically calculated rate constants for both the catalysts show that both NH3 and HCO2H catalyzed channels prefer a single hydrogen atom transfer path. Besides, both NH3 and HCO2H catalyzed paths have higher rate constant values as compared to that of the water catalyzed path.

High level ab initio calculations have been performed to predict the reaction energy and barrier height for the OH + HCl reaction. After including the effect of full quadratic excitations at the coupled cluster level, in addition to core, relativistic, spin-orbit, and diagonal Born-Oppenheimer corrections, we found the values of reaction energy and barrier height to be -15.29 and +2.38 kcal mol, respectively. Employing this reaction energy and barrier height, we used variational transition state theory in conjunction with small curvature tunneling to calculate the rate constants within a temperature range from 138 to 1000 K. The calculated rate constants were found to be in good agreement with available experimental results throughout the whole temperature range.

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A comprehensive investigation of the roles of acidic, neutral and basic catalysts in isomerization of methoxy radical in the troposphere has been carried out by quantum chemical calculations at the MP2 and CCSD(T) levels of theory. The effect of basic catalysts, namely ammonia and an ammonia-water complex, on the isomerization process has been studied for the very first time. In terms of rate coefficients ammonia was found to be a better catalyst than a water monomer whereas the ammonia-water complex was found to be more efficient over a water dimer but marginally less efficient than formic acid. Based on the effective rate constants under various tropospheric conditions, it was found that at 0 km altitude water dimers and ammonia-water complexes could compete with acid catalysts but at higher altitudes the acid catalysts would dominate their neutral and basic counterparts by a long distance.

In the present work, the catalytic effect of ammonia and formic acid on the CH3O˙ + O2 reaction has been investigated employing the MN15L density functional.