Gas-phase ion chemistry in the ternary SiH4-C3H6-NH3 system.

The gas-phase ion chemistry of propene-ammonia and silane-propene-ammonia mixtures was studied by ion trap mass spectrometry. As far as the binary mixture is concerned, the effect of different molar ratios of the reactants on the trend of ion species formed was evaluated, the ion-molecule reaction processes were identified and the rate constants for the main processes were measured. The results were compared with the collisional rate constants to determine the reaction efficiencies. In the ternary silane-propene-ammonia mixture the mechanisms of formation of Si(m)C(n)N(p)H(q)(+) clusters were elucidated and the rate constants of the most important steps were measured. For some species, selected by double isolation (MS/MS), the low abundance of the ions allowed us to determine the reaction paths but not the rate constants. Ternary ions are mainly formed by reactions of Si(m)C(n)H(q)(+) ions with ammonia, whereas a minor contribution comes from reactions of Si(m)N(p)H(q)(+) ions with propene. On the other hand, the C(n)N(p)H(q)(+) ions showed a very low reactivity and no step leading to ternary ion species was identified. The formation of hydrogenated ternary ions with Si, C and N has a basic importance in relation to their possible role as precursors of amorphous silicon carbides doped with nitrogen obtained by deposition from silane-propene-ammonia mixtures properly activated.