IR spectra of phenol +–(O 2) n cation clusters ( n = 1–4): Hydrogen bonding versus stacking interactions

Abstract

IR photodissociation spectra of phenol–(O 2) n cations, Ph +–(O 2) n , are recorded in the O–H stretch range ( ν OH). Two isomers of Ph +–O 2 are identified by their characteristic Δ ν OH shifts upon complexation, namely the H-bonded global minimum featuring a nearly linear O–H–O hydrogen bond (Δ ν OH = −86 cm −1) and the less stable π-bonded local minimum (Δ ν OH = +8 cm −1). The diradical character of O 2 has little influence on the Ph +–O 2 interaction. IR spectra of larger Ph +–(O 2) n clusters with n = 2–4 display a single ν OH band with small incremental blue shifts from ν OH of H-bonded Ph +–O 2 (Δ ν OH < 12 cm −1), indicating that these clusters have a single H-bond and ( n−1) π-bonds. Quantum chemical calculations support the interpretation of the experimental data.