The electric dipole moment of cobalt monoxide, CoO

A number of low-rotational lines of the E⁴Δ_7/2 ← X⁴Δ_7/2 (1,0) band system of cobalt monoxide, CoO, were recorded field free and in the presence of a static electric field. The magnetic hyperfine parameter, h_7/2, and the electron quadrupole parameter, eQq₀, for the E⁴Δ_7/2(υ = 1) state were optimized from the analysis of the field-free spectrum. The permanent electric dipole moment, μ_el, for the X ⁴Δ_7/2 (υ = 0) and E⁴Δ _7/2 (υ = 1) states were determined to be 4.18 ± 0.05 D and 3.28 ± 0.05 D, respectively, from the analysis of the observed Stark spectra of F′ = 7←F″ = 6 branch feature in the Q(7/2) line and the F′ = 8←F″ = 7 branch feature in the R(7/2) line. The measured dipole moments of CoO are compared to those from theoretical predictions and the trend across the 3d-metal monoxide series discussed.