Infrared spectroscopy of the benzene–H2O cluster cation: experimental study on the drastic structural change upon photoionization

Infrared photodissociation (IRPD) spectra of (benzene (Bz)–H2O)+ was measured in the 3 μm region. The cluster cations produced by two different methods, resonant photoionization of the neutral cluster and collisions of the bare benzene cation with water molecules, gave the same IR spectrum. This fact indicates that the most stable isomer cluster cation was generated in both methods. The cluster cation was found to have the side structure bound by the charge–dipole interaction. These results demonstrate that the water molecule on the benzene C6 axis in the neutral state is flipped to the side of the benzene ring upon the photoionization.