Determination of the proton affinities of bromo- and iodoacetonitrile using the kinetic method with full entropy analysis

The proton affinities bromo- and iodoacetonitrile are determined using a full implementation of the kinetic method, which includes calculation of the entropies. Branching ratios for dissociation of proton-bound dimers are measured for collision energies ranging from approximately 2 to 5 eV. Using a rigorously correct statistical approach, the proton affinities of bromo- and iodoacetonitrile are calculated to be 179.8 +/- 1.7 and 182.9 +/- 1.6 kcal/mol, respectively. It is shown that neglecting the entropy contributions for these systems leads to proton affinities that are too high by approximately 0.6 kcal/mol.