The model complexes CaXZ(L) (X = H, F L = Ne, Ar, Kr, Xe, CO, Nz) exhibit chemically significant interactions between the CaX2 fragment and the "inert-gas" ligand L. This is shown by ab initio calculations at the MP2 and CEPA 1 levels of theory using extended basis sets. Interaction energies of up to ca. 4-8 kcal/mol for L = CO, Nz and of ca. 1-3 kcal/mol for L = Kr, Xe have been calculated, and both the X-Ca-X angles and the Ca-X distances are affected by interaction with the ligand L. These

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... sults indicate that the interactions of floppy molecules like CaFz and inert-gas matrices compoaed of CO, Nz, or noble gases like Kr or Xe are nonnegligible, and the structures of the guest molecules may well differ from those of the free species. A numerical method is presented to recover the excimer formation rate coefficient from the experimental monomer and excimer decay curves. This method was applied to study pyrene monomer-excimer kinetics in cyclohexanol from 25 'C up to 85 OC. We observed that the time evolution of the rate coefficient deviates from the Smoluchowski equation, showing a minimum at high temperatures and concentrations, when the reversibility effects are more pronounced.