HCNq CO and HCOq CN formation

In order to investigate HCNq CO andror HCOq CN formation during the reaction of the ethynyl radical with nitric wx oxide we explore the potential energy surface of C HNO isomers via density functional theory. Product formation takes 2 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 q CO and involves a four-membered cyclic structure. Other pathways, involving formyl cyanide and leading to HCNq CO andror HCOq 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 kcalrmol which compares reasonably well with the reported value of 11.6 kcalrmol at the G2 level of theory. q 1998 Elsevier Science B.V.