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

Abstract

Mass-analyzed threshold ionization (MATI) has been used to prepare phenol cations in selected vibrational states, including the ground state. Reactions of ground state C6H5OH+ with ND3, studied in a guided ion-beam apparatus, are reported, along with related ab initio calculations. This paper focuses on the energetics and product branching in the proton transfer (PT) channel. 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 affinity for phenoxy radical of 208.7 kcal/mole, and a neutral PhO–H bond energy of 91.1 kcal/mole. The results are used to reinterpret previous dissociative photoionization studies of phenol-ammonia complexes.

Infrared photodissociation spectroscopy of protonated neurotransmitters in the gas phase – ARTICLE WITHDRAWN

“…The combination of excess energy from the 2-photon excitation process, ~100 kJ mol -1 , depending on the ionisation energy of the complex and the kinetic energy of the ejected photoelectron [39,40], with the energy released from the proton transfer reaction, ~50 kJ mol -1 , [43,44] Table Captions Table 1. Computed relative energies, dihedral angles and hydrogen bond distances/angles for protonated 1-phenyl ethylamine (PEA) and its complexes with the phenoxy radical: (i) MP2/6-311++G**//B3LYP/6-31+G*, (ii) B3LYP/6-31+G* optimisation.…”

Vibrational predissociation spectra of the Ar-tagged [CH4· H3O+] binary complex: spectroscopic signature of hydrogen bonding to an alkane

“…They observed that the spectral trends were consistent with the proton affinity correlation and concluded that the intermolecular proton bond was mostly electrostatic in nature. However, because the phenoxy radical has a rather large proton affinity (873 kJ mol À1 ) [20], it appears useful to study a system that will more readily donate an acidic proton. In addition, the open-shell electronic configuration of the radical introduces a possible complication because of the low-lying electronically excited state.…”

Dynamical control of ‘statistical’ ion–molecule reactions

“…MATI is, in principle, a general method. To date it has been used to rotationally select a number of diatomics [31,32] and to vibrationally select phenol cations [33].…”