Flash pyrolysis of silane, SiH4, and disilane, Si2H6, diluted in He or Ar (1%), was carried out at temperatures ranging from similar to 700 to similar to 1500 K. After a short reaction time of similar to 20 mus, the initial products were isolated in a supersonic molecular beam and detected by single vacuum ultra-violet (VUV) photon (lambda = 118 or 121 nm) ionization time-of-flight mass spectrometry (TOFMS). Initial decomposition and reaction products, both free radical intermediates and stable species, were directly observed, which included SiH2 and Si2H4. (C) 2001 Elsevier Science B.V. All rights reserved.