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

Resorcinol+–Arn cations (Rs+–Arn, n = 1,2) generated by resonant multiphoton ionization (REMPI) and electron ionization (EI) were assayed by their infrared (IR) photodissociation spectra in the OH stretch (νOH) range. Several isomers distinguished by their Ar ligand binding sites and their Rs+ isomeric cores are identified by characteristic ΔνOH complexation shifts. Neutral Rs–Arn complexes prefer intermolecular π-bonding of Ar to the aromatic ring, whereas cationic Rs+–Arn clusters show predominant H-bonding to the acidic OH groups. The REMPI-IR spectra of Rs+–Ar2 reveal νOH absorptions assigned to cold π-bound complexes and hot H-bound complexes. The latter are generated via ionization-induced intermolecular π → H isomerization.