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${\rm NH}_{2}\cdot +{\rm PH}_{3}\rightarrow {\rm NH}_{3}+{\rm PH}_{2}\cdot$ and${\rm H}\cdot +{\rm PH}_{3}\rightarrow {\rm H}_{2}\ {\rm PH}_{2}$. 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 decomposing in the mixture. This "protective" effect occurs at least partly via radical scavenging reactions.

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