IR photodissociation spectra of phenol-(O-2)(n) cations, Ph+ -(O-2)(n), are recorded in the O-H stretch range (v(OH)). Two isomers of Ph+-O-2 are identified by their characteristic Delta v(OH) shifts upon complexation, namely the H-bonded global minimum featuring a nearly linear O-H-O hydrogen bond (Delta v(OH) =- 86 cm(-1)) and the less stable pi-bonded local minimum (Delta v(OH) = +8 cm(1)). The diradical character of O-2 has little influence on the Ph+ - O2 interaction. IR spectra of larger Ph+ -( O2) n clusters with n = 2 - 4 display a single v(OH) band with small incremental blue shifts from v(OH) of H-bonded Ph+-O-2(Delta v(OH) < 12 cm(1)), indicating that these clusters have a single H- bond and ( n-1) pi-bonds. Quantum chemical calculations support the interpretation of the experimental data. (c) 2008 Elsevier B. V. All rights reserved.