Singlet–triplet anticrossings between the doubly excited 3 1K state and the g (3d) 3Σ+g state of H2

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Abstract
The 3 1K, v=1 level of H2 has recently been interpreted as an adiabatic mixture of vibronic levels of the EF 1Σs+ and the GK 1Σg+ double minimum states, with currently undetermined nonadiabatic corrections. Anticrossing spectra, which are sensitive to these state mixings, have been observed for the 3 1K, v=1, N level and the (3d) 3Σg+, v=1, N level of ortho-H2 for the rotational levels N=1 and 3. Linewidths, which are determined by either the singlet–triplet Fermi-contact hyperfine interaction or the spin–orbit interaction, as well as magnetic g values, help provide a detailed description of the 3 1K state. Measured singlet–triplet zero field separations are combined with previously published values to provide the best available value for the energy T0(a 3Σ) of the lowest triplet level (a 3Σ, v=0, N=0) with respect to the ground state, 95 076.36±0.20 cm−1.