Electric Resonance Spectrum and Dipole Moment of BaO

Abstract

The dipole moment of BaO in several vibrational states has been determined to be μ₀ = 7.955 D, μ₁ = .997 D, μ₂ = 8.039 D, μ₃ = 8.079 D with an error of ±0.003 D by the molecular‐beam electric‐resonance technique. The change of the dipole moment of BaO with vibrational state agrees with the change predicted by the Rittner model of classically polarizable ions. Measurement of relative intensities of vibrational lines yields a value of 680±100 cm⁻¹ for the vibrational frequency of the molecule and fourth‐order Stark effect yields a value of 0.304±0.007 cm⁻¹ for the rotation constant, in agreement with the more accurate spectroscopic determinations. The Ramsey method of separated oscillatory electric fields was used successfully in electric resonance, with the expected narrowing of linewidth. Because BaO is composed of spinless nuclei, it is proposed as the basis of a voltage or electric field standard that could have a precision of 1 part in 10⁸. A table of fourth‐order Stark coefficients is appended.