THEORETICAL-STUDY OF THE IONIZATION OF PHENOL-WATER AND PHENOL-AMMONIA HYDROGEN-BONDED COMPLEXES

The ionization of phenol-water and phenol-ammonia complexes have been determined both using ab initio methods that include electron correlat ion and the hybrid three-parameter B3LYP density functional method. Th e most stable structure of phenol-water cation corresponds to the C6H5 OH+-H2O non-proton-transferred complex. However, for the phenol-ammoni a cation the calculations indicate that the only minimum on the potent ial energy surface corresponds to the C6H5O-NH4+ proton transferred fo rm. The computed B3LYP adiabatic ionization potentials for C6H5OH-H2O and C6H5OH-NH3 have been determined to be 7.65 and 7.33 eV, respective ly. The results obtained indicate that, for the neutral H-bonded syste ms, the B3LYP density functional method yields very similar results to those obtained with the ab initio MP2 or MCPF methods. However, for t he ionized radical cations, B3LYP results compare much better with exp eriment and to the MCPF method than UMP2. The unsealed B3LYP vibration al frequencies are in very good agreement with the known experimental data.