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In three recent papers, the kinetics of the mercury photo-sensitized decomposition of ammonia and of deutero-ammonia have been compared in order (a ) to obtain the velocity coefficients for the processes occurring in these reactions, (b ) to establish correlations between these coefficients and the measured quenching radii and zero-point energy content of the molecules participating in the collisions. Calculations made upon simple premises yielded inconsistencies in the numerical values of the coefficients, thus throwing doubt upon the fundamental assumptions in the kinetic treatment of the problem. Evans and Taylor, in a later paper, have sought to surmount these difficulties by postulating the formation of mercury-ammonia complexes which have finite and different lifetimes for the two ammonias and which are subject to various deactivating collisions in the gas phase. There are, however, a number of factors to be taken into account, not hitherto considered, before recourse need be made to assumptions of this nature. It is the purpose of this paper to attempt to estimate quantitatively the magnitude of the corrections to be applied, to see then what discrepancies still exist and what probable explanations need be put forward to effect the necessary modifications to the scheme of reactions. We must distinguish between two separate phenomena occurring in these reactions. In the first place the ammonia molecule is dissociated by a collision with a mercury atom of high energy content and therefore, in order to calculate the velocity of this process, the stationary concentration of the mercury atoms as a function of ammonia and hydrogen pressure and other possible variables must be known. Secondly, the fragments of the dissociated molecule do not necessarily yield molecular hydrogen and nitrogen, for it is known in the direct photo chemical decomposition the quantum yield is less than unity and therefore reverse actions leading to the regeneration of ammonia must come into play. In comparing the behaviour of isotopic molecules, each of these factors may be different and hence they must be separately investigated. In the following pages the phenomena having to do with mercury atom collisions are described first and then the question of secondary reactions is considered in the second part of the paper.

The effect of imprisonment of resonance radiation in the decomposition of ammonia and of deutero-ammonia