Dynamics of small, ultraviolet-excited ICN- cluster anions.

The ultraviolet (UV) photodissociation of mass-selected ICN(-)Ar(n) and ICN(-)(CO2)n clusters (n = 0-5) is studied using a secondary reflectron mass spectrometer. Relative photodissociation cross sections of bare ICN(-) show the dominance of the I(-) photoproduct from 270 to 355 nm, the entire wavelength range studied. UV excitation populates both the (2)Σ(+) state that produces I* + CN(-) and the (2)Π states that produce I(-) + CN*. While the excited (2)Π states directly produce I(-), excitation to the (2)Σ(+) state also produces some I(-) product via nonadiabatic transitions to the (2)Π(1/2) state, which produces I(-) + CN. Partial solvation of the anion by Ar atoms or CO2 molecules alters the UV-branching percentages between the various dissociation channels: I* + CN(-) and I(-) + CN or I(-) + CN*. In addition, solvation by two or more Ar atoms or three or more CO2 molecules results in recombination, reforming ICN(-). Examination of the potential surfaces and transition moments in combination with the results of quantum dynamics calculations performed on the relevant excited states assist in the analysis of the experimental results.