Proton affinities of hydrogen halides determined by the molecular beam photoionization method

Gas-phase proton affinities of HF (95.5±1.4 kcal/mol), HCl (135±1 kcal/mol), and HBr (141±1 kcal/mol) have been measured along with the HX+–HX binding energies for the HCl and HBr systems (20±2 and 23±2 kcal/mol, respectively) by photoionization of van der Waals molecules produced in a supersonic expansion. A detailed discussion of the potentialities and limitations of the method is presented.