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 + SiMe 3 ] + , [M − X] + and (MeSi) 2 X + ions (X = Cl, Br or I). Dihalomethanes CH 2 X 2 form the most stable silylated molecular ions, whereas in the mass spectra of tetrahalomethanes (CX 4 ) these ions have not been detected and the ions CX 3 + are the most abundant. Production of bistrimethylsilyl‐halonium ions is the most pronounced process for haloforms (CHX 3 ).