GAS-PHASE ION-MOLECULE REACTIONS IN AMMONIA-METHYLSILANE MIXTURES STUDIED BY ION TRAPPING

The gas-phase reactivity of ammonia-methylsilane mixtures has been stu died by ion trap mass spectrometry. The mechanisms of ion-molecule rea ctions have been determined, and their rate constants measured and com pared with the corresponding collisional rate constants calculated acc ording 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 g ive the SiNHn+ (n = 2-4) and SiCNHn+ (n = 5, 6) ionic species in diffe rent reactions with NH3. Among them, SiNH4+ and SiCNH6+, which are the most abundant N-Si-containing ions, react further with ammonia to for m SiN2Hn+ (n = 5, 6) and SiCN2H9+ respectively. The most frequent path ways of silicon-containing ions reacting with ammonia correspond to el imination of H-2, or H, or adduct formation. Chain propagation proceed s mainly through ions of general formula SixCyHn+ in reactions with NH 3, while ions containing only silicon, nitrogen and hydrogen give spec ies, such as NH4+ and SiN2Hn+ (n = 5, 6), which do not react further.