Sarkar Saptarshi, Bandyopadhyay Biman
Department of Chemistry, Malaviya National Institute of Technology Jaipur, Jaipur 302017, India.
J Phys Chem A. 2020 May 7;124(18):3564-3572. doi: 10.1021/acs.jpca.0c00580. Epub 2020 Apr 28.
The gas-phase reaction of NO with NH 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 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 cm molecule s 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.
在对流层条件下，采用CCSD(T)/CBS//MP2/aug-cc-pVTZ理论水平的量子化学计算方法，对NO与NH的气相反应进行了研究。相对于孤立反应物，该反应的活化能垒为13.5 kcal/mol。使用Eckart隧穿的过渡态理论，在预平衡近似下进行了化学动力学计算，发现在298 K时速率系数为1.02×10⁻¹² cm³ molecule⁻¹ s⁻¹。为检验结果的可靠性，还使用了采用零曲率和小曲率隧穿的正则变分过渡态理论以及主方程进行计算。发现这些方法得到的结果与过渡态理论得到的结果一致。速率系数呈现正的温度依赖性，并且发现对于所有三种方法，其随温度的变化率非常相似。此外，还检验了速率系数的压力依赖性，发现在对流层条件下其压力依赖性可忽略不计。此外，所有电子结构计算均在CCSD(T)-F12/cc-pVTZ//M06-2X/aug-cc-pVTZ理论水平上进行，并使用这些结果计算了所有上述动力学模型的速率系数。发现结果与CCSD(T)//CBS//MP2/aug-cc-pVTZ结果非常吻合。
