Theoretical study of the CH3 + NS and related reactions: Mechanism of HCN formation

Abstract

More than thirty equilibrium and transition structures on the [CH3NS] potential energy surface have been located using the B3LYP/6-311+ + G(d,p) method. Thioformaldoxime (3) turns out to be the most stable isomer followed by thionitrone (2), a three-membered ring, thionitrosyl methane (1) and thiazyl methane. These isomers are connected to each other by 1,2H and 1,3H shifts and ring-chain rearrangement, but the associated energy barriers are rather high, making most of them stable with respect to unimolecular transformations. Starting from CH3+ NS, a possible initial atmospheric reaction, HCN formation appears to be the most favoured process through a cascade involvement of 1, 2 and 3. The standard heats of formation, Hf,2980, are calculated to be: 3, 149 kJ mol-1; and 1, 218 kJ mol-1; using the CCSD(T)/6-311+ + G(3df,2p) method, with an error of 10 kJ mol-1. © 1999 Taylor & Francis Ltd.