Kinetics and mechanisms for reactions of HNO with CH3 and C6H5 studied by quantum‐chemical and statistical‐theory calculations

Abstract

AbstractKinetics and mechanisms for the reactions of HNO with CH3 and C6H5 have been investigated by ab initio molecular orbital (MO) and transition‐state theory (TST) and/or Rice‐Ramsperger‐Kassel‐Marcus/Master Equation (RRKM/ME) calculations. The G2M(RCC, MP2)//B3LYP/6‐31G(d) method was employed to evaluate the energetics for construction of their potential energy surfaces and prediction of reaction rate constants. The reactions R + HNO (R = CH3 and C6H5) were found to proceed by two key product channels giving (1) RH + NO and (2) RNO + H, primarily by direct abstraction and indirect association/decomposition mechanisms, respectively. As both reactions initially occur barrierlessly, their rate constants were evaluated with a canonical variational approach in our TST and RRKM/ME calculations. For practical applications, the rate constants evaluated for the atmospheric‐pressure condition are represented by modified Arrhenius equations in units of cm3 mol−1 s−1 for the temperature range 298–2500 K: κ1A = 1.47 × 1011T0.76 exp[−175/T], κ2A = 8.06 × 103T2.40 exp[−3100/T], κ1B = 3.78 × 105T2.28 exp[230/T], and κ2B = 3.79 × 109T1.19 exp[−4800/T], where A and B represent CH3 and C6H5 reactions, respectively. Based on the predicted rate constant at 1 atm pressure for R + HNO → RNO + H, we estimated their reverse rate constants for R + HNO production from H + RNO in units of cm3 mol−1 s−1: κ−2A′ = 7.01 × 1010 T0.84 exp[120/T] and κ−2B′ = 2.22 × 1019 T−1.01 exp[−9700/T]. The heats of formation at 0 K for CH3NO, CH3N(H)O, CH3NOH, C6H5N(H)O, and C6H5NOH have been estimated to be 18.6, 18.1, 22.5, 47.2, and 50.7 kcal mol−1 with an estimated ±1 kcal mol−1 error. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 261–274, 2005