Size-dependent photodissociation cross sections for Sr+(NH3)n, n=3–6: Rydberg state formation and electron transfer

Abstract

We report photodissociation cross sections for the mass‐selected cluster ions Sr⁺(NH₃)_n, with n in the range from 3 to 6. The cross sections exhibit large redshifts that increase monotonically with increasing cluster size. For the n=3 cluster, the absorption cross section peaks near 700 nm, while the n=6 cluster spectrum appears to reach a maximum at 1.5 μm, in the near infrared region of the spectrum. A spectral moment analysis of the cross sections shows that <r²≳ for the ground state electronic radial distribution increases by an order of magnitude over the cluster size range from 1 to 6 solvent molecules. In conjunction with path integral Monte Carlo calculations carried out by Martyna and Klein, we argue that the increase in <r²≳ is diagnostic of the increasing Rydberg character of cluster states that correlate with 5s and 5p atomic orbitals on Sr⁺. An analysis of the charge transfer to solvent process as described by a thermodynamic Born cycle suggests that the rapid stabilization of solvated ion‐pair states with increasing cluster size provides a plausible mechanism for introducing Rydberg character into cluster valence states based on 5s/5p atomic ion orbitals.