Electronic Structure of SrO

Abstract

Molecular‐beam electric‐resonance spectra of SrO are measured in the rf and microwave regions. The microwave transitions are induced with a frequency‐broadened klystron, greatly reducing the time needed to search for resonances. Rf‐microwave double resonance is used to establish the vibrational assignment of the rf spectra from the known assignment of the microwave spectra. The dipole moment and rotation constant of ⁸⁸Sr¹⁶O in the lowest two vibrational states are: μ₀=8.900 D, μ₁=8.874 D, B₀=0.33688 cm⁻¹, and B₁=0.33469 cm⁻¹. These rotation constants show that this ¹Σ state is identical with the lower state of three optical‐emission systems of SrO. With the aid of a molecular‐beam magnetic‐deflection experiment, it is shown that this state is almost certainly the ground electronic state of SrO. The evidence indicating triplet ground or low‐lying states in SrO and the other alkaline‐earth oxides is reviewed, and it is concluded that in no alkaline‐earth oxide has a triplet ground state been established. SrO has the largest percent ionic character, μ/er, yet observed for any diatomic molecule. The dipole‐moment function μ(r) of SrO differs considerably from that of BaO and cannot be explained by a model of two polarizable ions. A description of the bonding in the alkaline‐earth oxides can be obtained from comparisons of recent SCF calculations on LiF and BeO.