The deflection by an electrostatic quadrupole of molecular beams of SiO2, TiO2, ZrO2, CeO2, ThO2, TaO2, and UO2 has been measured. Of the above species only SiO2 was found to be nonpolar while the remaining species were found polar. This sequence (with the exception of TaO2 and UO2) together with CO2 forms an isoelectronic sequence with previously investigated alkaline-earth difluorides. In each instance the geometry of isoelectronic partners is similar.
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.
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