Electronic structure of Ne₂ below the first ionization limit

Results from new laser excitation spectra of ²⁰Ne₂ have been combined with previously published experimental and theoretical data to provide a consistent picture describing many of the Rydberg states observed below the first ionization limit. These states are found to fall mainly into Rydberg series converging on the ...3σ_u Χ ²Σ_u⁺ ground core of Ne₂ ⁺. Spectral data for the npσ ³Σ _g⁺ and npπ 3Π_g ← α 3Σ_u⁺ and npπ 3Π_g ← α 3Σ_u⁺ series support the current assignments of the upper states. Although (0-0) bands dominate these series, other vibronic transitions are observed. The 6-23pσ 3Σ_g⁺ -α(0-0) bands are more perturbed than the npπ ³Π _g -α(0-0) series; hence, data for 4-17pπ 3Π_g⁺ -α (0-0) and 4-6fλ( ³Σ_g⁺ , 3Π_g ⁺)-α(0-0) were used to determine a value of 34 409 ± 2 cm ^-1 for the lowest ionization limit of ²⁰Ne₂. Rotational constants for the ν = 0 levels of 4-17pi; ³Π _g and 10-23pσ ³Σ_g⁺also are presented.