Ab initio study of the ClO+NH2 reaction: Prediction of the total rate constant and product branching ratios

Abstract

The mechanism for ClO + NH2 has been investigated by ab initio molecular orbital and transition-state theory calculations. The species involved have been optimized at the B3LYP/6-311+G(3df,2p) level and their energies have been refined by single-point calculations with the modified Gaussian-2 method, G2M(CC2). Ten stable isomers have been located and a detailed potential energy diagram is provided. The rate constants and branching ratios for the low-lying energy channel products including HCl + HNO, Cl + NH2O, and HOCl + (NH)-N-3 (X-3 Sigma(-)) are calculated. The result shows that formation of HCl + HNO is dominant below 1000 K; over 1000 K, Cl + NH2O products become dominant. However, the formation of HOCl + (NH)-N-3 (X-3 Sigma(-)) is unimportant below 1500 K. The pressure-independent individual and total rate constants can be expressed as k(1)(HCl + HNO) = 4.7 x 10(-8)(T-1.08) exp((-129)/(T)), k(2)(Cl + NH2O) = 1.7 x 10(-9)(T-0.62) exp((-24)/(T)), k(3)(HOCl + NH) = 4.8 x 10(-29)(T-5.11) exp((-1035)/(T)), and k(total) = 5.0 x 10(-9)(T-0.67) exp((-1.2)/(T)), respectively, with units of cm(3) molecule(-1) s(-1), in the temperature range of 200-2500 K.