FLASH PHOTOLYSIS OF HYDROGEN IODIDE IN PRESENCE OF DEUTERATED HYDROCARBONS

The reactions of hot hydrogen atoms in the range 0.8-2.4 eV with perdeuterated and partially protonated hydrocarbons have been studied. The hot atoms were produced in C2D6, C3D8, n-C4D10, and various isotopically mixed ethanes by flash photolyzing HI-RD and HI-RHD mixtures. Graphs of product ratio H2/HD vs the initial reactant ratio HI/RD were characteristically linear. These and similar graphs for mixtures containing a rare gas were analyzed using the kinetic theory of hot-atom reactions developed by Estrup and Wolfgang and also by a simpler approach. Where comparison was possible, the results of the two methods of analysis showed good agreement. The following parameters were evaluated: average relative reaction probabilities for H*-HI and H*-RD collisions (where the asterisk denotes the hot species), the fraction of H* moderated to that reacting hot in pure RD, and β, the average fractional energy loss by H* is collision with RD. The most important conclusions which can be drawn from the results are: (a) a simple interpretative scheme employing average reaction and moderation probabilities serves to give nearly quantitative estimates of the parameters involved; (b) in all cases the probability of H* reaction with HI is considerably larger than with RD, although several times smaller than the corresponding reaction probabilities of thermal hydrogen atoms; (c) deuterium abstraction by H* from the six partially deuterated ethanes is simply statistical; (d) collisions between H* and RD are quite inelastic, the values for β being greater than 4, 6, and 12 times the respective rigid-sphere values for perdeuterated ethane, propane, and n-butane.