Gas-phase ion-molecule reactions in ammonia-methylsilane mixtures studied by ion trapping

The gas-phase reactivity of ammonia-methylsilane mixtures has been studied by ion trap mass spectrometry. The mechanisms of ion-molecule reactions have been determined, and their rate constants measured and compared with the corresponding collisional rate constants calculated according to the average dipole orientation theory. The SiCHn+ (n = 2-5) and SiHn+ (n = 0-3) primary ions react with methylsilane according to the previously reported self-condensation processes. These ions also give the SiNHn+ (n = 2-4) and SiCNHn+ (n = 5, 6) ionic species in different reactions with NH3. Among them, SiNH4+ and SiCNH6+, which are the most abundant N-Si-containing ions, react further with ammonia to form SiN2Hn+ (n = 5, 6) and SiCN2H9+ respectively. The most frequent pathways of silicon-containing ions reacting with ammonia correspond to elimination of H-2, or H, or adduct formation. Chain propagation proceeds mainly through ions of general formula SixCyHn+ in reactions with NH3, while ions containing only silicon, nitrogen and hydrogen give species, such as NH4+ and SiN2Hn+ (n = 5, 6), which do not react further.