INFRARED LASER-INDUCED PHOTOFRAGMENTATION OF SIZE-SELECTED SF6.(CO2)N-11( CLUSTER IONS, FOR N IN THE RANGE 2)

New observations on the IR excitation and fragmentation of heterogeneo us cluster ions of the form Y.X(n)+ are present. In the system discuss ed here, SF6 . (CO2)n+, the circumstances are such that IE[SF6] > 1E[C O2)n]; therefore, we can be confident that the positive charge resides on the cluster. As a result, it becomes possible to study the IR spec troscopy of a neutral chromophore in association with a series of mass -selected clusters. Two photofragmentation channels are identified for SF6-(CO2)n+, loss of SF6 dominates in small clusters, but the loss of a single CO2 moleule gains in probability as the clusters increase in size. By monitoring these separate photofragmentation channels in con junction with absorption spectra, relationships can be identified betw een frequency shifts, line shapes, decay dynamics and cluster size. A statistical model has been used to reproduce the fragmentation pattern seen for the two decay channels, and as a result the relative binding energies of SF6 and CO2 have been estimated as a function of cluster size. From an analysis of all the data it is concluded that, in the la rger cluster ions, the SF6 molecule is held rigid in a single site whe re it is away from the positive charge, but partially solvated by the CO2 molecules.