The methylsilylidyne (SiCH3, X(2)A") and the silenyl (H2CSiH, X(2)A') radicals were identified via infrared spectroscopy in low temperature silane-methane matrices upon irradiation of the samples matrices with energetic electrons at 10 K. The v(4) and v(3) fundamentals of the methylsilylidyne species were detected at 1226 and 1371 cm(-1), whereas one band of the silenyl radical showed lip at 822 cm(-1)(v(6)). These assignments were verified in partially deuterated matrices. Our studies suggest that these radicals are generated through radiolysis of silene (H2CSiH2, X(1)A(1)) and its methylsilylene isomer (CH3SiH, X(1)A'). The new absorptions of two SiCH3 isomers can be utilized in future spectroscopic studies of chemical vapor deposition processes and in astronomical searches of silicon-bearing organometallic molecules to better understand the chemistry of the circumstellar envelope of the carbon star IRC + 10216. (c) 2005 Elsevier B.V. All rights reserved.