IR spectra of phenol+–Krn cluster cations (n = 1,2): Evidence for photoionization-induced π → H isomerization

Phenol+–Kr cations (PhOH+–Kr) generated by photoionization (REMPI) of the neutral complex and in an electron ionization (EI) source were assayed by their infrared (IR) spectra in the OH stretch (νOH) range. Two isomers are identified in the EI–IR spectrum by their ΔνOH complexation shifts: the more stable H-bound global minimum (ΔνOH = −123 cm−1) and the less stable π-bound local minimum (ΔνOH = +1 cm−1). The REMPI–IR spectrum reveals νOH absorptions assigned to cold π-bound complexes and hot H-bound dimers. The latter are generated via π → H isomerization after the ionization of neutral π-bound dimers. EI–IR spectra are also presented for PhOH+–Kr2. Quantum chemical calculations support the interpretation of the spectroscopic data.