Extensive spectra attributable to transitions from the 4sσ a 3Σ+ metastable state of Ar2 to excited Rydberg states have been observed by intracavity absorption spectroscopy and by laser excitation spectroscopy in the afterglow of a pulsed corona discharge. Of these the most extensive and best resolved were the laser induced fluorescence spectra. Most of the spectra can be assigned to vibronic transitions in the nfλ (3Πg, 3Σg +) and npλ(3Πg,3Σ g+) ← a 3Σu+ series. The 5pπ 3Πg ← a 3Σ u+ and 7pσ 3Σg + ← a 3Σu+ transitions observed near 19 823 and 19 529 cm-1, respectively, exhibit many bands with v′ ≠ 0 in their (v′-v″) vibrational band system developments. The higher n value members of these and other observed series are dominated by (0-0) transitions. Rotational structure is partially resolved in a few bands of the 7pσ 3Σg+ -a system, but most of the spectra observed appear to be either rotationally unresolved or made up of blended collections of rotational lines. Above the 7pσ, 5pπ pair, the (n + 2)pσ 3Σg + and npπ 3Πg members of the npλ series rapidly coalesce, indicating a rapid onset of decoupling of the electronic orbital angular momentum, L, from the internuclear axis. Such decoupling leads to np-complex formation at n values much lower than observed in the npλ series of the lighter dimers: He2 and Ne2. From the data for the observed series, the lowest ionization limit of Ar 2 (relative to a 3Σu+,v = 0) was determined to be 29 373 ± 3 cm-1. Vibrational intervals ΔG(v + 1/2) for a 3Σu+ (v≤4) and 7pσ 3Σg+ (v≤2) yield the vibrational constants ωe = 296 and 282 cm-1 and xωe = 2.5 and 17 cm-1, respectively.
ASJC Scopus subject areas
- Physics and Astronomy(all)
- Physical and Theoretical Chemistry