Chemistry of nuclear recoil 18F atoms. X. Studies of 18F caged capture processes in CH3CF3/H2S and CH3CHF2/H2S liquid mixtures

Absolute nuclear recoil 18F yields have been determined for liquid-phase fluoroethane/H2S mixtures at H2S concentrations ranging to 50 mol %. The results have been interpreted using contrasting Miller-Dodson and steady-state nonthermal kinetic formulations. The Miller-Dodson collision densities do not change significantly with the addition of H2S. Nonthermal rate coefficients are closely comparable and independent of mixture composition for F-to-HF reactions with H2S, CH3CF3, and CH3CHF2, exceeding by roughly fivefold the composite values that include all fluoroethane organic reaction channels. Branching ratios for 18F energetic bimolecular vs. caging reactions are independent of H2S concentration. In contrast with the predictions of collision-theory cage-effect models, efficient F-to-HF reactions do not interfere with primary caged capture. Reaction probability functions for energetic F-to-HF processes in H2S and fluoroethanes are crudely similar and extend to center-of-mass energies of 25 eV or more