Rotational analysis of the 7pσ ³Σ_g ⁺←a³Σ_u⁺ system of the Ar₂ molecule

Rotationally resolved transitions from the metastable 4sσ a ³Σ_u⁺ state of Ar₂ to the 7pσ 3Σ_g⁺ state have been observed by laser excitation spectroscopy in a pulsed corona discharge. Laser induced fluorescence spectra for the 7pσ ³Σ_g⁺← a³Σ_u⁺ transition observed near 19 530 cm^-1 have led to the first resolved triplet splittings and rotational analyses for Rydberg-Rydberg transitions in Ar₂. Analyses for the (0-0), (0-1), (1-0), and (1-1) bands of 7pσ←a are presented here. Bands with v′=2 are observed for this system but exhibit no rotational structure and bands with v′>2 are not observed, indicating that the predissociation lifetimes of these upper levels fall rapidly for v′>1. Data presented lead to rotational energies and molecular constants for the a³Σ_u⁺ and 7pσ ³Σ _g⁺ states, including the effective rotational constant B_e which is determined to be 0.1412 cm^-1 and 0.1345 cm^-1 for the 4sσ a³Σ_u⁺ and 7pσ 3Σ_g⁺ states, respectively. Results are compared to ab initio and other calculations, and combined with existing data to produce experimental estimates of D₀ and D_e for the a³Σ_u⁺ state of 5700±200 cm ^-1 and 5850±200 cm^-1, respectively.