Experimental and theoretical study of the photofragmentation process: Ar3++hν→Ar2++Ar

An experimental study of the photofragmentation of Ar3+ at wavelengths >650 nm has been undertaken in order to investigate the reaction channel Ar3++hν→Ar2++Ar. As a function of photon energy, measurements have been made of the Ar+/Ar2+ branching ratio and the relative kinetic energy of the photofragments. A steady decline observed for the latter as a function of decreasing photon energy, suggests that the dimer ions emerges from the photodissociation processes with a very high level of internal excitation. Supporting semiclassical calculations of the decay dynamics confirm the trend seen for the Ar+/Ar2+ branching ratio, but do not reproduce the quantitative details. The calculations do, however, provide strong support for an experimental analysis of the energetics of fragmentation, and show that Ar2+ can appear either in the electronic ground state, but with a very high degree of vibrational excitation, or in the weakly bound Πg2 electronic excited state.