Infrared laser-induced photofragmentation of size-selected SF 6·(CO 2) +n cluster ions, for n in the range 2–11

Abstract

New observations on the IR excitation and fragmentation of heterogeneous clusters ions of the form Y·X + n are present. In the system discussed here, SF 6·(CO 2) + n , the circumstances are such that IE[SF 6] > IE[CO 2) n ]; therefore, we can be confident that the positive charge resides on the cluster. As a result, it becomes possible to study the IR spectroscopy of a neutral chromophore in association with a series of mass-selected clusters. Two photofragmentation channels are identified fo SF 6·(CO 2) + n , loss of SF 6 dominates in small clusters, but the loss of a single CO 2 molecule gains in probability as the clusters increase in size. By monitoring these separate photofragmentation channels in conjunction with absorption spectra, relationships can be identified between 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 SF 6 and CO 2 have been estimated as a function of clusted size. From an analysis of all the data it is concluded that, in the larger cluster ions, the SF 6 molecule is held rigid in a single site where it is away from the positive charge, but partially solvated by the CO 2 molecules.