The Radiation Chemistry of Phosphine-Ammonia Mixtures in the Gas Phase

Irradiation of gaseous mixtures of ammonia and phosphine with Co-60 gamma rays yields hydrogen, red phosphorus, and nitrogen. Attempts to find other products have been unsuccessful. Hydrogen yields are larger than predicted from the assumption of an ideal mixture, in which the ammonia and phosphine decompose proportionately to the dose each absorbs, but nitrogen yields show a striking depression. This occurs even in mixtures with less than 0.1 mole percent phosphine. Phosphine appears to be acting as an efficient radical scavenger, via reactions such as NH₂· + PH₃→ NH₃+ PH₂· and H· + PH₃→ H₂ PH₂. The phosphino radical reacts further to yield (finally) phosphorus and hydrogen. By comparing the radiolytic decomposition of ammonia in a mixture containing a few mole percent phosphine and in the pure state, it can be shown that roughly one phosphine is removed for each ammonia that is prevented from decomp...