| Summary: | The photodissociation dynamics of alkali-ammonia clusters in the gas phase have been explored using a combination of photofragmentation spectroscopy and velocity map imaging. Electronic excitation of Li(NH3)4 to the A∼2T2 state leads to the production of relatively slow photofragments with a high degree of internal excitation, which is consistent with internal conversion to the ground electronic state of Li(NH 3)4, followed by slow, statistical decay. At low excitation energies, the dominant decay channel yields Li(NH3) 3 + NH3, but at higher energies, Li(NH3) 2 is the dominant lithium-containing photoproduct. There is evidence of a barrier in the exit channel that manifests itself as a maximum in the total kinetic energy release (TKER) distribution observed at low kinetic energy. Modeling of the TKER distribution for the Li(NH3)4 → Li(NH3)3 + NH3 process suggests an upper limit of 3750 ± 150 cm-1 for the Li-N bond dissociation energy and a barrier height of ∼150 ± 50 cm-1. © 2011 American Chemical Society.
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