Fine structure of 3s,3d: 3Σ, 3Π, 3Δ complex of H2 by Doppler-free, laser spectroscopy

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Abstract
We have used the method of Doppler‐free laser spectroscopy to resolve, for the first time, the fine structure of the H2, 3s,3d complex: h (3s)3Σ g +, g (3d)3Σ g +, i (3d)3Π g , and j (3d)3Δ g . A collimated beam of H2 molecules in the metastable c 3Π u state was crossed with a tunable, dye laserbeam. The absorbed light quenched the metastable molecules and changed the detected molecular beam intensity. The 3s,3d fine structure intervals have been measured to an accuracy of a few MHz (∼0.0001 cm−1) for all of the rotational levels in the v=0, 1 levels, which are connected by allowed transitions to the N=2 rotational level of the c (2p)3Π u state of parahydrogen. The fine structure constants of the N=1 rotational level of the i (3d)3Π g − state, extrapolated to the equilibrium internuclear separation are A π+γ=−145±4MHz and B π 0−√6B π 2=958±13MHz and MHz. These results are discussed in terms of the transition from united to separated atom values. The remaining states are coupled to each other by configuration interaction and rotational interactions. By parametrizing such interactions, we find that an account of the fine structure of these states can be given by considering only interactions within the triplet 3s, 3d complex. With only one exception, interactions with states outside this complex do not have to be taken into account. This analysis gives values for 15 spin interaction constants.

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