Radiation-Induced Transformations of Isolated Phosphine Molecules at Cryogenic Temperatures: Spectroscopic and Chemical Aspects

The radiation-induced transformations of isolated phosphine molecules in a series of solid noble gas matrices occurring under the action of X-rays at 4.5 K were studied by FTIR spectroscopy. It was shown that decomposition was quite efficient (the corresponding radiation-chemical yields of PH3 degradation were estimated as 5.8, 4.2, 3.5, and 2.0 molecules per 100 eV for neon, argon, krypton, and xenon, respectively). The radiolysis proceeds via two channels yielding PH2• and PH, respectively (the spectroscopic and kinetic data suggest that the latter species is partially trapped in the same cage with hydrogen molecules). Comparative studies using direct activation of isolated phosphine molecules in matrices at λ = 185 nm revealed similarity in the degradation pathways under radiolysis and VUV photolysis. Spectroscopic characteristics of the observed products and possible astrochemical implications of the results are discussed.