SiBr4, SiCl4, (CH3) SiCl3, (CH3) 2SiCl2, (CH3) 3SiCl, C2H3SiCl3, C6H5SiCl3, (C6H5) 2SiCl2, (CeH5) 3SiCl, and (C6H5) 4Si have been γ-irradiated in a matrix of 2-methyltetrahydrofurane at — 196 °C. The reactivity towards the free electron is shown to decrease with increasing number of methyl groups and to increase with increasing number of phenyl groups in these compounds. The results are compared with mass spectrometric appearance potential measurements. The products formed in the electron attack show absorption bands in the near ultraviolet and infrared. Some of the absorptions can easily be bleached by blue light. The observed absorptions are attributed to the following molecular anions or neutral radicals formed by non-dissociative or dissociative electron captures respectively: (C6H5)4Si⊖, (C6H5)3SiCl ⊖, (C6H5)2SiCl, C6H5SiCl2, CH2=CHSiCl2 CH3SiCl2, SiCl3, SiBr3 .