Stark effect, polarizabilities and the electric dipole moment of heteronuclear diatomic molecules in 1Σ states

Abstract

The theory of second-order Stark effect in 1Σ states of heteronuclear diatomic molecules is thoroughly reviewed. The rigorous treatment given demonstrates that by introducing rotational, vibrational and electronic branch polarizabilities, the intrinsic character of the second-order Stark effect in diatomic molecules can be shown to be related more closely to polarizabilities than to dipole moments. The well-known expression for the Stark shift in 1Σ levels which is dominated by the square of the dipole moment is only a crude, though sufficient approximation whenever large dipole moments are involved. For small dipole moments, however, this approximation is likely to fail, leading to an erroneous determination of such dipole moments. In the limiting case of negligible influence of the molecular rotation on the vibronic matrix elements, the arithmetic mean of the electronic branch polarizabilities turns out to be equal to the well-known static electronic polarizabilities α ∥ and α ⊥. The results are applied to the interpretation of the Stark splitting in the A 1Σ +, υ′ = 5, J′ = 1 level of 7LiH, recently determined by Stark quantum-beat spectroscopy.