Further Studies of Reactions of Hot Hydrogen with Hydrocarbons

A further quantitative examination of the reactions of recoil tritium with hydrocarbons has been made. Reaction probabilities for various types of processes have been determined as a function of neon moderation. Data have been analyzed using the kinetic theory of hot reactions. This theory has been extended to indicate the relative mean energies and overlap of the excitation functions for the several possible reactions. The following conclusions are indicated by our data: (1) Reactivity integrals $I$ and energy loss parameters $\alpha$ increase with increasing complexity of the reactant molecule. This appears to be associated with the greater ability of larger molecules to absorb the excess energy of hot tritium atoms. (2) Abstraction appears to occur at higher average energies than displacement. Since abstraction is known to be dominant at lower energies, this means that it can also occur efficiently at higher energies than displacement. These findings accord with a previously postulated stripping mechanism for abstraction and with the observed effect of bond energy on this process. (3) Displacement reaction is restricted to a relatively narrow energy range in methane but can extend to higher energies in higher hydrocarbons.