Shock Wave and Theoretical Modeling Study of the Dissociation of CHF. I. Primary Processes.

The unimolecular dissociation of CHF leading to CF + H, CHF + HF, or CHF + H is investigated by quantum-chemical calculations and unimolecular rate theory. Modeling of the rate constants is accompanied by shock wave experiments over the range of 1400-1800 K, monitoring the formation of CF. It is shown that the energetically most favorable dissociation channel leading to CF + H has a higher threshold energy than the energetically less favorable one leading to CHF + HF. Falloff curves of the dissociations are modeled. Under the conditions of the described experiments, the primary dissociation CHF → CHF + HF is followed by the reaction CHF + HF → CF + H. The experimental value of the rate constant for the latter reaction indicates that it does not proceed by an addition-elimination process involving CHF* intermediates, as assumed before.