The temperature dependence of hydrogen abstraction reactions: F+HCl, F+HBr, F+DBr, and F+HI

A laser photolysis/infrared fluorescence technique has been used to study the temperature dependence of the F+HCℓ, F+HBr, F+DBr, and F+HI absolute rate constants in the range from 195 to 373 °K. Multiphoton dissociation of SF6 with a TEA CO2 laser was used to provide a transient concentration of fluorine atoms. Their subsequent reaction with hydrogen donors was monitored by observing the appearance rate of HF(v?1) through its infrared fluorescence. The observed rate constants show a marked nonlinear Arrhenius behavior which is consistent with a model in which reaction takes place both vai direct attack by the fluorine atom at the hydrogen end of HX and via formation of a collision complex FXH which rearranges to FHX and then dissociates to HF and X products.