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

✍ Scribed by Y. M. Choi; M. C. Lin

• Publisher: John Wiley and Sons
• Year: 2005
• Tongue: English
• Weight: 192 KB
• Volume: 37
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20079

✦ Synopsis

Abstract

Kinetics and mechanisms for the reactions of HNO with CH~3~ and C~6~H~5~ 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 = CH~3~ and C~6~H~5~) 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 cm^3^ mol^−1^ s^−1^ for the temperature range 298–2500 K: κ~1A~ = 1.47 × 10^11^T^0.76^ exp[−175/T], κ~2A~ = 8.06 × 10^3^T^2.40^ exp[−3100/T], κ~1B~ = 3.78 × 10^5^T^2.28^ exp[230/T], and κ~2B~ = 3.79 × 10^9^T^1.19^ exp[−4800/T], where A and B represent CH~3~ and C~6~H~5~ 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 cm^3^ mol^−1^ s^−1^: κ~−2A′~ = 7.01 × 10^10^ T^0.84^ exp[120/T] and κ~−2B′~ = 2.22 × 10^19^ T^−1.01^ exp[−9700/T]. The heats of formation at 0 K for CH~3~NO, CH~3~N(H)O, CH~3~NOH, C~6~H~5~N(H)O, and C~6~H~5~NOH 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