Spectrum and Structure of the He2 Molecule. V. Characterization of the Triplet States Associated with the UAO's 6− 17pπ and 7− 12pσ

The electronic transitions 6 − 17pπ 3Πg→2s a 3Σu+ and 7 − 12pσ 3Σg+→2s a 3Σu+ of He2 are described and the previously unreported npσ 3Σg+ and 11 − 17pπ 3Πg states characterized. Existing data for the triplet states associated with the UAO's npπ and npπ are summarized and discussed. The N = 0, v = 0 level of the 2s a 3Σu+ state (the lowest stable electronic state for He2) is found to lie 34,302.2 ± 0.1 cm−1 below the v = 0 level of the X 2Σu+ state of He2. From extrapolation of the molecular constants for the npπ 3Πg− series, approximate values for the ground state of He2+ are ωe ≅ 1698.5cm−1, xωe ≅ 35.25cm−1, Be ≅ 7.211 cm−1, and re ≅ 1.0806 Å. “Accidental pure pecession” between the state pairs npΠ 3Πg+ and n + 1 pσ 3Σg+ is identified as the major (although not exclusive) perturbation systematically affecting the rotational levels of the npλ components with plus systmmery.