Multiphoton studies of jet‐cooled Xe2 near the Xe*5d[5/2]03 state: Characterization of the ground and excited state potential curves

Xe2 gerade Rydberg states observed in the afterglow of a microplasma by laser spectroscopy of a(3)Σ(+)(u)(1(u), O(-)(u)) 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 A(1)Σ(+)(u)(O(+)(u)) --> X(1)Σ(+)(g)(O(+)(g)) emission in the vacuum ultraviolet (∼172 nm), induced by laser excitation of Ω(g) ← a(3)Σ(+)(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 Ω(g) ← a(3)Σ(+)(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(5p(6) (1)S0) + Xe(5p(5) 6p) and built on a predominantly A(2)Π3/2g molecular ion core. Specifically, the spectroscopic constants for the upper state of the 1(g) ← 1(u), O(±)(u) absorptive transitions are determined to be Te = 13,000 ± 150 cm(-1), ω'(e) = 120 ± 10 cm(-1), ω'(e)x'(e) = 1.1 ± 0.4 cm(-1), De = 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)1g and (3)O(+)(g) states of Xe2. These spectra exhibit the most extensive vibrational development, and provide evidence for the first molecular core-switching transition, observed to date for any of the rare gas dimers at small R (<4 Ǻ). 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.

Photoelectron imaging of several 5d and 6p Rydberg states Xe2 and improving the Xe2(+) I(1∕2g) potential

Velocity map photoelectron imaging was used to study the photoionization of Xe(2) in several low-lying 5d and 6p Rydberg states. The Rydberg states were prepared by two-photon excitation and ionized by either one additional photon from the pump laser (2+1 ionization), or by one photon of a second color (2+1(') ionization). The 2+1 images and associated photoelectron spectra were consistent with previous results, although some adjustment of previously proposed equilibrium bond lengths was necessary to fit the spectra with Franck-Condon factor calculations. The 2+1(') images provided higher resolution photoelectron spectra and, in conjunction with the Xe(2)(+) potentials reported by Zehnder and co-workers [J. Chem. Phys. 128, 234306 (2008)] and the 6p and 5d Xe(2)∗ potentials calculated by Jonin and Spiegelmann [J. Chem. Phys. 117, 3059 (2002)], provided a means for improving the Xe(2)∗ potentials. New experimental data are also presented for photoionization populating the Xe(2)(+) I(1∕2g) state, and are used to provide a better description of its potential curve.

Rydberg states of the rare gas dimers

This work is dedicated to Gerhard Herzberg and his prodigious contributions to molecular spectroscopy. Of particular relevance here is Herzberg's seminal 1987 article (Annu. Rev. Phys. Chem. 38, 27 (1987)) in which he discussed the electronic structures of several groups of molecules he termed "Rydberg molecules". Among these are the rare gas dimers (Rg2), a group whose study has benefited significantly from recent advances in laser excitation and synchrotron-based spectroscopies, as well as in theory. Following the spirit of Herzberg's 1987 article, this paper reviews some of the more prominent features of Rydberg states in the Rg2 family as viewed from the current perspective.Key words: rare gas dimers, rare gas dimer excited states, Rg2 electronic structures, Rydberg states of He2, Ne2, Ar2, Kr2, and Xe2, electronic states of He2, Ne2, Ar2, Kr2, and Xe2.