Formation mechanisms of protonated benzophenone (BP) were investigated in BP/toluene(Tol) and BP/ethanol(EtOH) binary cation clusters by a resonant enhanced multiphoton ionization (REMPI) time-of-flight mass spectrometry. [(BP)H](+) and [(BP)(2)H](+) are produced by intracluster ion-molecule reactions after REMPI of Tol via the S-1 or BP via the S-n in BPn(Tol)(m) clusters. In a BP/EtOH system, [(BP)H(EtOH)(n)](+) are generated after the REMPI of BP and undergo hydrogenation in the aromatic rings by the subsequent photoexcitation. The dominant products are [(BP)H-3(EtOH)(n)](+) and [(BP)H-8(EtOH)(n)](+), which appear in smaller and larger clusters, respectively. Structures of protonated BP's and intracluster reactions were discussed based on quantum chemical calculations. (C) 2003 Elsevier B.V. All rights reserved.