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The diatomic collisional intermediate responsible for the formation of an electronically excited molecule by teratomic recombination has been observed in both the spectral and temporal domains by laser spectroscopy. We report experiments demonstrating thermal Xe(6s[3/2]2)-Xe(5p6 1S0) atomic collision pairs to be the immediate precursor to the formation of Xe*2(a³Σ+u, A¹Σ+u) by the three body process: Xe*(6s)+2Xe → Xe*2 + Xe, where the asterisk denotes an excited electronic state. Photoassociating Xe(6s)-Xe atomic pairs by free ← free transitions of the collision complex interrupts the production of the electronically excited Xe dimer, thereby suppressing Xe2 spontaneous emission in the vacuum ultraviolet (VUV, λ ~ 172 nm, A¹Σ+u → X¹Σ+g). Intercepting Xe(6s)-Xe pairs before the complex is stabilized by the arrival of the third atom in the teratomic collision process selectively depletes the pair population in a specific Franck-Condon region determined by the probe laser wavelength (λ). Measurements of the variation of VUV emission suppression with λ provide a spectral signature of the [Xe(6s[3/2]2) - Xe(¹S0)]* complex and map the probe laser wavelength onto the thermal energy (∊″) of the incoming collision pairs. [ABSTRACT FROM AUTHOR]

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 A¹Σu+ (Ou+) → X¹Σg+ (Og+) emission in the vacuum ultraviolet (∼172 nm), induced by laser excitation of Ωg ← a³Σu+ (1u,Ou-) [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 ← a³Σu+ 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 A²Π3/2g molecular ion core. Specifically, the spectroscopic constants for the upper state of the 1g ← 1u,Ou± absorptive transitions are determined to be Te = 13 000 ± 150 cm-1, ωe′ = 120 ± 10 cm-1, ωexe′ = 1.1 ± 0.4 cm-1, De = 3300 ± 300 cm-1, and ΔRe = Re′- Re″ = 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)1g and (3)Og+ 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]