Spectroscopic studies of mass selected clusters of Sr+ solvated by H2O and D2O

Abstract

In this paper we present the results of spectroscopic studies on mass selected Sr + (H 2 O) n , n=1–4 and Sr + (D 2 O) n , n=1–6 clusters. Mass spectra of nascent clusters formed in our laser vaporization source show that hydrated metal ion species are predominant for n⩽4. Clusters larger than this size are more abundant in the hydrogen loss form SrOH + (H 2 O) n−1 . The cluster size at which the product switching occurs is slightly larger (n=5) in the deuterated species. Photodissociation of all clusters results in both ligand loss and H/D atom loss occurring via an intracluster reaction. The monomer and dimer cluster species exhibit distinct absorption bands attributable to electronic excitation of the 5s valence electron of Sr + . Metal–ligand stretching frequencies are extracted from Franck–Condon progressions in the excited state.Spectroscopic parameters agree well with ab initio calculations [Bauschlicher et al., J. Chem. Phys. 96, 4453 (1992), and Sodupe et al., Chem. Phys. Lett. 212, 624 (1993)]. Analysis of the product branching ratios allows us to conclude that, when below the threshold for excited state dissociation, rapid internal conversion followed by an intracluster reaction preferentially occurs on the ground state surface, while evaporation occurs primarily in the excited state. We find evidence in the spectral profiles of clusters with n⩾3 for a consistent “substructure” characterized by a pπ state lacking σ-type interactions with the ligand molecules.