Competition between stacking and hydrogen bonding: theoretical study of the phenol center dot center dot center dot Ar cation and neutral complex and comparison to experiment

Experimental results obtained previously for vdW-bonded and H-bonded phenol center dot center dot center dot argon (PhOH center dot center dot center dot Ar) complexes in their S-0 and D-0 states are combined with ab initio quantum-chemical theoretical results. Such a combination allows us to present a complete'' description of the geometry, relative energies, interaction energies and enthalpies of PhOH center dot center dot center dot Ar complexes. Based on a minimum-energy-path study, the transition structures and barrier heights related to transitions between stable conformers are also presented. For the presented structures, the agreement between the theoretical interaction enthalpy at 0 K with experimentally obtained values is very good. On the other hand, for numerical harmonic-frequency calculations we find a very poor performance for the neutral PhOH center dot center dot center dot Ar complex and complete failure for the studied complexes in their cationic form.