tailieunhanh - Thermokinetic study of the isomerization of isocyanic acid

In this work, the detailed study on the mechanism, kinetics and thermochemistry of the isomerization of isocyanic is described. Theoretical study was carried out by ab initio molecular orbital theory based on the CCSD(T) and B3LYP/6-311++G(3df,2p) methods in conjunction with statistical theoretical kinetic Rice-Ramsperger-KasselMarcus (RRKM) Master equation calculations. | Vietnam Journal of Chemistry, International Edition, 55(4): 478-483, 2017 DOI: Thermokinetic study of the isomerization of isocyanic acid Nguyen Huu Tho Sai Gon University Received 7 December 2016; Accepted for publication 28 August 2017 Abstract In this work, the detailed study on the mechanism, kinetics and thermochemistry of the isomerization of isocyanic is described. Theoretical study was carried out by ab initio molecular orbital theory based on the CCSD(T) and B3LYP/6-311++G(3df,2p) methods in conjunction with statistical theoretical kinetic Rice-Ramsperger-KasselMarcus (RRKM) Master equation calculations. The potential energy surface (PES) for the isomeric reactions was also examined. At 760 Torr pressure, temperature dependent rate constants of the isomeric reactions HNCO HOCN (a), HNCO H(CNO) (b) and HNCO H(NCO) (c) were: k(T) (a) = , k(T) (b) = , k(T) (c) = respectively. Calculated results show that the isomerization of isocyanic acid may take place via three mechanisms and have very high barriers; all rate constants of them are very small in the temperature range from 300 to 2000 K. Keywords. Potential energy surface, isocyanic acid, density function theory, isomerization. 1. INTRODUCTION Isocyanic acid (HNCO) is known as the simplest organic compound which has full four most important biogenic elements C, H, N, O in organic chemistry. This molecule has sixteen valence electrons, symmetric group CS. Its electronic configuration in ground state is given by (1a’)2(2a’)2(3a’)2(4a’)2(5a’)2(6a’)2(7a’)2(1a”)2(8a’)2( 9a’)2(2a”)2(10a’)0 [1, 2]. In daily life, the major source forming isocyanic acid is from tobacco smoke, biomass burning, fuel burning at low temperature, forest fires, etc. At concentration over 1 ppbv (parts per billion by volume), isocyanic acid can cause cataract, heart failure and other chronic diseases efor .