Xe2 gerade Rydberg states observed in the afterglow of a microplasma by laser spectroscopy of a³Σu+(1u,Ou-) absorption in the green (545-555 nm) and near-infrared (675-800 nm).

Bound←bound transitions of the Xe dimer at small internuclear separation (R < 4.0 Å) have been observed in the 545-555 nm and 675-800 nm spectral regions by laser spectroscopy in the afterglow of a pulsed Xe microplasma with a volume of ∼160 nl. Transient suppression of Xe₂ A¹Σ_u⁺ (O_u⁺) → X¹Σ_g⁺ (O_g⁺) emission in the vacuum ultraviolet (∼172 nm), induced by laser excitation of Ω_g ← a³Σ_u⁺ (1_u,O_u^-) [Rydberg←Rydberg] transitions of the molecule, has confirmed the existence of structure between 720 and 770 nm (reported by Killeen and Eden [J. Chem. Phys. 84, 6048 (1986)]) but also reveals red-degraded vibrational bands extending to wavelengths beyond 800 nm. Spectral simulations based on calculations of Franck-Condon factors for assumed Ωg ← a³Σ_u⁺ transitions involving Ω = 0±,1 gerade Rydberg states suggest that the upper level primarily responsible for the observed spectrum is an Ω = 1 state correlated, in the separated atom limit, with Xe(5p⁶ ¹S₀) + Xe(5p₅ 6p) and built on a predominantly A²Π_3/2g molecular ion core. Specifically, the spectroscopic constants for the upper state of the 1g ← 1_u,O_u^± absorptive transitions are determined to be T_e = 13 000 ± 150 cm^-1, ω_e′ = 120 ± 10 cm^-1, ω_ex_e′ = 1.1 ± 0.4 cm^-1, D_e = 3300 ± 300 cm^-1, and ΔR_e = R_e′- R_e″ = 0.3 ± 0.1 Å which are in general agreement with the theoretical predictions of the pseudopotential hole-particle formalism, developed by Jonin and Spiegelmann [J. Chem. Phys. 117, 3059 (2002)], for both the (5)1_g and (3)O_g⁺ states of Xe₂. These spectra exhibit the most extensive vibrational development, and provide evidence for the first molecular coreswitching transition, observed to date for any of the rare gas dimers at small R (<4 Å). Experiments in the green (545-555 nm) also provide improved absorption spectra, relative to data reported in 1986 and 1999, associated with Xe₂ Rydberg states derived from the Xe(7p) orbital. [ABSTRACT FROM AUTHOR]