Surface-induced reactions of acetone cluster cations

Formation of HCN+ in collisions of N+ and N2+ with a self-assembled propanethiol surface on gold

Collisions of N⁺ and N₂⁺ 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 N₂⁺ 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.

Formation of HCN+ in heterogeneous reactions of N2(+) and N+ with surface hydrocarbons

A significant increase of the ion yield at m/z 27 in collisions of low-energy ions of N₂⁺ and N⁺ with hydrocarbon-covered room-temperature or heated surfaces of tungsten, carbon-fiber composite, and beryllium, not observed in analogous collisions of Ar⁺, is ascribed to the formation of HCN⁺ in heterogeneous reactions between N₂⁺ or N⁺ and surface hydrocarbons. The formation of HCN⁺ in the reaction with N⁺ indicated an exothermic reaction with no activation barrier, likely to occur even at very low collision energies. In the reaction with N₂⁺, the formation of HCN⁺ was observed to a different degree on these room-temperature and heated (150 and 300 °C) surfaces at incident energies above about 50 eV. This finding suggested an activation barrier or reaction endothermicity of the heterogeneous reaction of about 3–3.5 eV. The main process in N₂⁺ or N⁺ interaction with the surfaces is ion neutralization; the probability of forming the reaction product HCN⁺ was very roughly estimated for both N₂⁺ and N⁺ ions to about one in 10⁴ collisions with the surfaces.

Surface-induced dissociation and chemical reactions of C2D4(+) on stainless steel, carbon (HOPG), and two different diamond surfaces

Surface-induced interactions of the projectile ion C(2)D(4)(+) with room-temperature (hydrocarbon covered) stainless steel, carbon highly oriented pyrolytic graphite (HOPG), and two different types of diamond surfaces (O-terminated and H-terminated) were investigated over the range of incident energies from a few eV up to 50 eV. The relative abundance of the product ions in dependence on the incident energy of the projectile ion [collision-energy resolved mass spectra, (CERMS) curves] was determined. The product ion mass spectra contained ions resulting from direct dissociation of the projectile ions, from chemical reactions with the hydrocarbons on the surface, and (to a small extent) from sputtering of the surface material. Sputtering of the surface layer by low-energy Ar(+) ions (5-400 eV) indicated the presence of hydrocarbons on all studied surfaces. The CERMS curves of the product ions were analyzed to obtain both CERMS curves for the products of direct surface-induced dissociation of the projectile ion and CERMS curves of products of surface reactions. From the former, the fraction of energy converted in the surface collision into the internal excitation of the projectile ion was estimated as 10% of the incident energy. The internal energy of the surface-excited projectile ions was very similar for all studied surfaces. The H-terminated room-temperature diamond surface differed from the other surfaces only in the fraction of product ions formed in H-atom transfer surface reactions (45% of all product ions formed versus 70% on the other surfaces).