Ex situ Fourier transform infrared spectroscopic data are presented for the decomposition of cyanoethylphosphine (CYEP), benzylphosphine (BZP), cyclopentylphosphine (CPP), and mixtures of these phosphines with trimethylindium (TMIn) under atmospheric pressure metallorganic chemical vapor deposition (MOCVD) conditions using dihydrogen carrier gas. IR bands due to CYEP, BZP, CPP, TMIn, and their decomposition products have been monitored as a function of susceptor temperature. The decomposition of CYEP, BZP, and CPP alone in dihydrogen commenced at temperatures >723, 723, and 823 K, respectively, while in the presence of TMIn the onset of decomposition occurred at the lower temperatures of 623, 523, and 573 K, respectively In afl cases the decomposition was accompanied by the formation of phosphine and related hydrocarbons which may be attributed to the operation of either beta-elimination or free-radical reaction mechanisms. In the presence of TMIn a room temperature prereaction was observed for all precursors, the only detectable products of which were methane and involatile solids or liquids. By comparison with previous data obtained for cyclohexylphosphine and tertiarybutylphosphine it is suggested that the involatile solids formed in the presence of TMIn are polymers of the type [MeIn-PR]n and we propose that the extent of organophosphine prereaction with TMIn is governed by a combination of steric factors influencing the extent of polymerization and the stability of the species resulting from cleavage of the P-C bond.