Kinetic Theory of Hot-Atom Reactions. II. Evaluation of Collisional Energy Loss. Application to Reactive Mixtures

Abstract

The kinetic theory of reactions of atoms of high translational energy undergoing moderating collisions is further developed. The nature and validity of the assumptions underlying the treatment and the range of applicability of the final expressions are discussed in detail. It is shown that experimental data on the total probability of reaction in which the hot atom is chemically bound can be used to evaluate two fundamental quantities: (1) the reactivity integral, or reaction probability integrated over energy on a logarithmic scale (I) ; (2) a measure of average energy transfer in collisions of hot atoms with the reactive species (α). The present treatment involves no variable or arbitrary parameters. As a result sufficient data may be obtained to provide stringent internal consistency tests of the applicability of the model and its assumptions to any given system. Two types of systems are specifically treated: (1) a single reactant moderated by inert gas; (2) competitive reactions in systems of two reactants. The relative utility of such systems for determination of the basic parameters α and I is discussed. Examples of the use of the expressions developed to calculate average logarithmic collisional energy loss (α) are given. Recent data of Colebourne on interaction of hot F with CF₄, and data of Root and Rowland on hot H in mixtures of D₂ and CH₄ are used. The α's derived indicate that moderating collisions in these media are highly inelastic. Root and Rowland's hypothesis that CH₄ is a better moderator than D₂ is quantitatively confirmed. The implications of these findings for the mechanism of hot‐atom processes are briefly discussed.