Nature of Isomeric-Transition-Induced Bromine-82 Reactions with CH4 and CD4

The role of excess kinetic energy and thermal processes in the ⁸²Br reaction in gaseous CH₄ and CD₄ activated by ^82mBr isomeric transition (IT) was determined using rare‐gas and bromine additives. Possible isotope effects were investigated between (n, γ‐induced ⁸⁰Br and ^80mBr and between CH₄ and CD₄ target molecules. The “freeze–thaw” technique and $\mathrm{(n,\; \gamma )}$ “in‐reactor” technique were employed in determining the ⁸²Br organic yields. The effects of He, Kr, Xe, and Br₂ additives on the reaction of CH₄ and CD₄ with ⁸²Br activated by the (IT) process are presented. The data appear to extrapolate, at zero mole fraction CH₄, to 3.7% ± 0.5% for the He, Kr, and Xe additives and to 0% for Br₂. This would indicate that 7.4% minus 3.7% is formed via excess kinetic‐energy processes and that 3.7% of the organic ⁸²Br is formed via thermal (kinetic‐energy‐independent) processes, probably involving Br⁺ ions in their first two excited states, ${}^3{P}_1$ and ${}^3{P}_0$ . The data suggest the absence of a target molecule isotope effect between CH₄ and CD₄ in the ⁸²Br(IT)‐activated process, but does suggest a target molecule isotope effect for (n, γ‐activated bromine reactions. The data for bromine reactions involving excess kinetic energy were analyzed using the kinetic theory of hot reactions. The reactivity integral values $I$ were found to be very low. The kinetic theory showed good internal consistency for (IT)‐activated bromine reactions. Experimental data showed the absence of any isotope effect between (n, γ‐induced ^80mBr and ⁸⁰Br reaction in CH₄. The use of HBr as a source molecule was reinvestigated in the CD₄ system and found to give organic yields higher than those of Br₂ systems at low mole fractions. This difference diminished at higher HBr concentrations.