Photodissociation spectroscopy of benzene cluster ions in ultraviolet and infrared regions: Static and dynamic behavior of positive charge in clusterions

Photodissociation spectroscopy is applied to benzene cluster ions in ultrav iolet and infrared regions. In the ultraviolet photodissociation spectrum o f (C6H6)(3)(+) , a characteristic broad band emerges at 255 nm. This band i s assigned to a pi*<-- pi transition of a solvent benzene molecule that exi sts in the trimer. This is in accordance with the previous model of the ion cluster with a dimer ion core and a solvent benzene molecule. The infrared photodissociation spectra of (C6H6)(n)(+) (n=3-5) show a sharp band at 306 6 cm(-1). The band is attributed to a C-H stretching vibration of the dimer ion core. The infrared spectra of (C6H6)(n)(+) (n=3-5) are fitted to the m odel spectra reproduced by combining the C-H stretching bands of the dimer ion core and the solvent benzene molecule. The infrared photodissociation s pectra of mixed benzene trimer ions with one or two benzene-d(6) molecules demonstrate that there is no correlation between the excited dimer ion core site in the trimer and the photofragment dimer ion species. This implies t hat a dimer ion core switching occurs in photoexcited vibrational states pr ior to the dissociation. (C) 2001 American Institute of Physics.