HETEROGENEOUS REACTIONS BETWEEN NITROGEN IONS AND HYDROCARBONS ATTACHED TO SOLID SURFACES

Formation of HCN+ in heterogeneous reactions between gas phase ions N+, N-2(+), and NH+ with hydrocarbons adsorbed on conducting substrates (tungsten, beryllium, carbon) was investigated at room temperature, and at elevated temperatures of 150 degrees C and 300 degrees C of the surface. The incident energy range of the ions was 20-100 eV. The reaction with N+ was observed at all incident energies and it may be expected to occur even down to thermal energies, though this extrapolation is tentative and not confirmed by experiments. The reaction with N-2(+) was observed only at incident energies above about 60 eV, and the reaction with NH+ at incident energies above about 40 eV, indicating an endothermicity or an activation barrier of about 3-3.5 eV (N-2(+)) or 2.8-3.2 eV (NH+). Only the reaction with N+ may thus be of a possible relevance to astrophysics and the upper atmosphere of Titan.