Fine structure, hyperfine structure, and Stark effect in the NO A 2Σ+ state by optical radio-frequency double resonance

Abstract

Using the Se I 1961 Å spectral line to pump the J = 3/2 component of the v = 3, N = 1 level of the NO A ²Σ⁺ state, we observe the zero‐field rho‐doubling hyperfine transitions by optical radio‐frequency double resonance. The Stark shift of one of the resonance components is measured to determine the permanent electric dipole moment. An analysis of the resonance line shapes yields the following molecular constants: The rho‐doubling constant γ = −82.91±0.03 MHz; the hyperfine parameters of the ¹⁴N nucleus b = 40.29±0.07 MHz, c = 2.25±0.11 MHz, and eqQ = −2.88±0.17 MHz; and the dipole moment μ = 1.10±0.03 D, where all errors represent three standard deviations. The value of γ is explained reasonably well by calculations of the A−X spin‐orbit mixing from which we conclude that variations of γ with v and N are small. The values of the hyperfine parameters b and c are within 6% and 18% of recent CI calculations by S. Green, while the less well determined values of eqQ differ by about a factor of 2. The measured dipole moment differs considerably from the CI value, μ = 0.40±0.10 D. We speculate on possible explanations for this surprisingly large discrepancy.