化学
热化学
反应速率常数
动力学
氢原子萃取
激进的
物理化学
过渡态理论
甲基自由基
氢
大气温度范围
从头算
二氧化氮
化学动力学
计算化学
热力学
有机化学
物理
量子力学
作者
Б. М. Брудник,Dorota Wójcik-Pastuszka,Jerzy T. Jodkowski
摘要
In this study a theoretical analysis of the kinetics and thermochemistry of the gas phase reaction between methyl mercaptan and nitrogen dioxide is presented. The molecular properties (optimized geometries, vibrational levels, and rotational constants) of the reactants and products were derived from ab initio calculations. The relative total energies of the molecular structures taking part in the reaction kinetics were examined at the G3 level. The rate constants of the elementary steps and their dependence on temperature were evaluated using transition-state theory and a version of the statistical adiabatic channel model. The mechanism of the reaction CH 3 SH +NO 2 is complex and the first elementary step is related to hydrogen abstraction. The derived analytical expressions for the rate constants k 1a = 7.9×10 ―15 ×(T/300) 1.90 ×exp(―8190/T) and k 1b = 6.0×10 ―13 ×(T/300) 1.94 ×exp(―16290/T) cm 3 molecule ―1 s ―1 describe the kinetics of the hydrogen abstraction reactions CH 3 SH +NO 2 → CH 3 S + HNO 2 (1a) and CH 3 SH +NO 2 → CH 2 SH + HN0 2 (1 b), respectively, in the temperature range of200-500 K. The CH 3 S and CH 2 SH radicals formed can undergo subsequent radical-radical (2a-c) and radical-N0 2 (3a,b) recombination reactions with rates determined by the high-pressure limiting rate constant, expressed as k 2a,∞ (CH 3 S + CH 3 S) = 4.0×10 ―11 ×(T/300) 0.20 , k 2b,∞ (CH 3 S + CH 2 SH) = 1.2×10 ―10 ×(T/300) 0.15 , k 2c,∞ (CH 2 SH + CH 2 SH) = 6.7×10 ―11 ×(T/300) 0.19 , k 3a,∞ (CH 3 S+NO 2 )=1.3×10 ―11 (T/300) 0.19 , and k 3b,∞ (CH 2 SH + NO 2 ) = 2.6×10 ―11 ×(T/300) 0.23 cm 3 molecule s ―1 . Values of the calculated rate constants are in good agreement with available results of kinetic measurements.
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