Theoretical studies on C2H+NO reactions: mechanism for HCN+CO and HCO+CN formation

In order to investigate HCN+CO and/or HCO+CN formation during the reaction of the ethynyl radical with nitric oxide we explore the potential energy surface of [C2HNO] isomers via density functional theory. Product formation takes place via several isomerization steps after the initial adduct formation. We identified one reaction pathway resulting in fragmentation that is accessible without activation of the initial reactants; this path forms HCN+CO and involves a four-membered cyclic structure. Other pathways, involving formyl cyanide and leading to HCN+CO and/or HCO+CN, require initial activation. Wherever possible, our calculated energies are compared with higher level ab initio results. The heat of formation of formyl cyanide is calculated to be 14.4 kcal/mol which compares reasonably well with the reported value of 11.6 kcal/mol at the G2 level of theory.