A number of low-rotational lines of the E4Δ ← X4Δ (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,  , and the electron quadrupole parameter,  , for the E4Δ(υ = 1) state were optimized from the analysis of the field-free spectrum. The permanent electric dipole moment, μ⃗ el , for the X4Δ (υ = 0) and E4Δ (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 ′ = 7 ← = 6 branch feature in the (7/2) line and the ′ = 8 ←  = 7 branch feature in the (7/2) line. The measured dipole moments of CoO are compared to those from theoretical predictions and the trend across the 3-metal monoxide series discussed.

http://dx.doi.org/10.1063/1.4868551