Proton transfer in the [phenol-NH3](+) system: An experimental and ab initio study

Mass-analyzed threshold ionization (MATI) has been used to prepare phenol c ations in selected vibrational states, including the ground state. Reaction s of ground state C6H5OH+ with ND3, studied in a guided ion-beam apparatus, are reported, along with related ab initio calculations. This paper focuse s on the energetics and product branching in the proton transfer (PT) chann el. Based on thermochemistry in the literature, combined with calculations of the intracomplex PT barrier, PT was expected to make up a large fraction of the total reactive scattering. Experimentally, it is found that PT has a small cross section with clear threshold behavior, and the conclusion is that the PT reaction is endoergic by 4.5 +/- 1 kcal/mole. Assuming that NH3 has a proton affinity of 204.0 kcal/mole, this results in a proton affinit y for phenoxy radical of 208.7 kcal/mole, and a neutral PhO-H bond energy o f 91.1 kcal/mole. The results are used to reinterpret previous dissociative photoionization studies of phenol-ammonia complexes. (C) 2000 American Ins titute of Physics. [S0021-9606(00)00413-X].