Gerade Rydberg states of Xe₂ probed by laser spectroscopy in the afterglow of a Xe microplasma: Ω_g ← a³ Σ_u⁺ ( 1_u, O_u^- ) transitions in the near-infrared (675-800 nm)

Gerade Rydberg states of Xe₂ lying 12 500-14 800 cm^-1 above the a³ Σ_u⁺ ( 1_u, O_u^- ) metastable levels of the dimer have been observed by laser spectroscopy in the afterglow of a Xe microplasma with a volume of ∼160 nL. Photoexcitation of Ω_g ← a³ Σ_u⁺ ( 1_u, O_u^- ) (Rydberg ← Rydberg) state transitions at small internuclear separations ( R ≃ R_e ( Xe₂⁺ ) ) while monitoring the suppression of Xe₂ ( O_u⁺ → O_g⁺ ) spontaneous emission in the ultraviolet confirms the presence of an extensive series of red-degraded vibrational bands in the 675-800 nm region that are tentatively identified with an Ω = 1 upper state with a molecular ion core having predominantly B²Π_3/2g character. Spectral simulations yield the following constants for the 1_g state: R_e^′ = 3.49 ± 0.1 Å, T_e = 12 980 ± 70 cm^-1, ω_e^′ = 122 ± 3 cm^-1, ω_e^′ x_e^′ = 0.9 ± 0.2 cm^-1, and D_e^′ = 2250 ± 70 cm^-1.