Chemical ionization mass spectrometry of halomethanes with tetramethylsilane as reagent gas

Chemical ionization mass spectra of halomethanes measured using tetramethylsilane as reagent gas exhibit three major peaks corresponding to [M + SiMe3]+, [M − X]+ and (MeSi)2X+ ions (X = Cl, Br or I). Dihalomethanes CH2X2 form the most stable silylated molecular ions, whereas in the mass spectra of tetrahalomethanes (CX4) these ions have not been detected and the ions CX3+ are the most abundant. Production of bistrimethylsilyl‐halonium ions is the most pronounced process for haloforms (CHX3).