The gas-phase chemical species produced from both the direct decomposition of 1,1,3,3-tetramethyl-1,3disilacyclobutane (TMDSCB) on a tungsten filament and the secondary reactions in the HWCVD reactor were identified by vacuum ultraviolet laser single-photon ionization coupled with time-of-flight mass spectrometry. TMDSCB decomposes on the filament to methyl and 1,1,3-trimethyl-1,3-disilacyclobutane-1-yl radicals. Subsequent hydrogen abstraction reactions from the parent molecule by methyl radicals and biradical combination reactions are dominant in the reactor. The formation of dimethylsilene (m/z = 72) through the ring Si-C bond cleavage is indirectly confirmed by the observation of the signal from 1,1,3,3,5,5-hexamethyl-1,3,5-trisilacyclohexane at m/z = 216. Tetra- and tri-methylsilane are also found to be formed in the HWCVD reactor. (C) 2009 Elsevier B.V. All rights reserved.