Formation of HCN in collisions of N and N with a self-assembled propanethiol surface on gold.

Collisions of N and N with C3 hydrocarbons, represented by a self assembled monolayer of propanethiol on a polcrystalline gold surface, were investigated by experiments over the incident energy range between 5 eV and 100 eV. For N, formation of HCN is observed at incident energies of projectile ions as low as 20 eV. In the case of N projectile ions, the yield of HCN increased above zero only at incident energies of about 50 eV. This collision energy in the laboratory frame corresponds to an activation energy of about 3 eV to 3.5 eV. In the case of N projectile ions, the yield of HCN was large for most of the incident energy range, but decreased to zero at incident energies below 20 eV. This may indicate a very small energy threshold for the surface reaction between N and C3 hydrocarbons of a few tenths of an eV. Such a threshold for the formation of HCN may exist also for collisions of N with an adsorbed mixture of hydrocarbon molecules.