Absorption spectra of sizehyphen;selected solvated metal cations: Electronic states, symmetries, and orbitals in Sr+(NH3)1,2and Sr+(H2O)1,2

摘要

This paper presents photodissociation spectra for the solvated metal ion clusters Sr+(NH3)1,2and Sr+(H2O)1,2from 420 to 740 nm in the visible region of the spectrum. The spectra have a banded structure, corresponding to transitions from ground electronic states based upon the2Sconfiguration of the Sr+ion to excited states based primarily uponphyphen;orbitals of the excited Sr+. The photodissociation cross sections are large, sim;10minus;17ndash;10minus;16cm2. For the same solvent, spectral band positions are only weakly dependent upon the degree of solvation. We show that a dramatic reduction in intensity of the second excited state band in the Sr+(NH3)2spectrum suggests that this state has strong atomic iondhyphen;orbital parentage and that the molecule is centrosymmetric. Photodissociation of the H2O solvated species proceeds through three excited electronic states corresponding principally to three different orientations of the metalporbitals with respect to solvent symmetry axis. Absorption band positions for Sr+(H2O)2are shifted slightly from those of Sr+(H2O) and the presence of a substantial unstructured continuum appears in the doubly solvated ion. The absorption spectra for the Sr+(H2O)1,2species are significantly bluehyphen;shifted and narrowed relative to those of Sr+(NH3)1,2, an observation that is understood through simple molecular orbital diagrams incorporating the fact that the ionization potential of H2O is 2.4 eV larger than that of NH3.