Extensive spectra attributable to transitions from the 4sO" a 3~ + metastable state of Ar 2 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 nf:i eITg,3~t) and np:i eITg/~g+).-a 3~u+ series. The 5P1T 3IT g .-a 3~u+ and 7pO" 3~g+ .-a 3~: transitions observed near 19 823 and 19 529 cm -I, respectively, exhibit many bands with v' =f 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 7pO" 3~g+ -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 7pO", 5P1T pair, the (n + 2)pO" 3~g+ and np1T 3ITg members of the np:i series rapidly c9,alesce, 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 np:i series of the lighter dimers: He 2 and Ne2' From the data for the observed series, the lowest ionization limit of Ar2 (relative to a 3~u+ ,v = 0) was determined to be 29 373 ± 3 cm -I.Vibrational intervals 6.G(v + 112) for a 3~u+ (v<4) and 7pO" 3~g+ (v<2) yield the vibrational constants {J)e = 296 and 282 cm -I and x{J)e = 2.5 and 17 cm -I, respectively.