EVIDENCE FOR A PRECURSOR TO DECOMPOSITION FOR PHOSPHINE ADSORPTION ON RH/AL2O3 SURFACES

Transmission infrared spectroscopy has been used to detect formation of the species PH2 and PH upon PH3 adsorption and decomposition on Al2O3-supported Rh surfaces. In addition, a unique bonding configuration of PH3 has been identified that is a precursor to this decomposition process. The precursor state displays a v(PH3) vibration that is shifted considerably to lower wavenumbers with respect to the chemisorbed state due presumably to two-center bonding. The population of the precursor state is a sensitive function of temperature, exposed surface metal sites, and surface pretreatment, and precedes the initial phosphine decomposition. The P-H stretching vibration characteristic of this precursor state is quite distinct from that of physisorbed PH3, chemisorbed PH3, or the partial decomposition fragments, PH2 and PH. © 1990 American Chemical Society.