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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. [ABSTRACT FROM AUTHOR]

The gas-phase reaction of N 2 O 5 with NH 3 under tropospheric conditions has been carried out employing quantum chemical calculations at the CCSD(T)/CBS//MP2/aug-cc-pVTZ level of theory. The activation barrier of the reaction was found to be 13.5 kcal mol -1 with respect to isolated reactants. Chemical kinetic calculations were carried out under pre-equilibrium approximation using transition-state theory employing Eckart tunneling, and the rate coefficient was found to be 1.02 × 10 -24 cm 3 molecule -1 s -1 at 298 K. To check the reliability of the result, calculations have also been carried out using the canonical variational transition-state theory employing both zero- and small-curvature tunneling as well as the master equation. The results obtained from these methods were found to be consistent with those obtained from the transition-state theory. The rate coefficient was found to show positive temperature dependence, and its rate of change with temperature was found to be very similar for all three methods. Further, the pressure dependence of the rate coefficient has been checked and it was found that it shows negligible pressure dependence under tropospheric conditions. Besides, all of the electronic structure calculations have been carried out at the CCSD(T)-F12/cc-pVTZ//M06-2X/aug-cc-pVTZ level of theory and the rate coefficients using all of the above-mentioned kinetic models have been computed using these results. The results were found to match closely with the CCSD(T)//CBS//MP2/aug-cc-pVTZ results.