Observation of ns ³∑_u⁺ (1_u, 0_u^-) → mp ³Π₉ Rydberg transitions of Ar₂ (n = 4; 5≤n≤15) and Kr₂(n = 5; 6≤n≤16) in absorption

Rydberg series of Ar₂ and Kr₂ have been observed in the visible and ultraviolet (350≤Aλ560 nm) absorption spectra of the lowest-lying metastable states of the dimer (ns ³∑ _u⁺ (1_u, 0_u^-); Ar: n = 4, Kr: n = 5). The most prominent series for Ar₂ and Kr₂ are assigned to ns ³∑_u⁺ → mp ³Πg (Ar: 5≤m≤15; Kr: 6≤m≤16) Rydberg transitions of the diatomic molecule and adiabatic ionization potentials are determined from an extrapolation of the series to their limits (m → ∞) to be 116 356 ± 340 cm^-1 (14.43 ± 0.04 eV) for Ar₂ and 104 616 ± 150 cm^-1 (12.97 ± 0.02 eV) for Kr₂. The dissociation energies of the A ²∑_u⁺ [1 (1/2)_u] dimer ion states of Ar₂ and Kr² are, therefore, 1.33 ± 0.04 and 1.03 ± 0.02 eV, respectively. All of the observed Rydberg states have an A ²∑_u⁺ ion core. Binding energies of the lowest observed 3Π_g states, were determined to be (1.331 ± 0.005) eV for Ar₂ and (1.030 ± 0.001) eV for Kr₂. The quantum defects for the Ar ₂ and Kr₂ series ( 1.656 ± 0.006 and 2.621 ± 0.004, respectively) and ω_e - 2ω_ex _e for the ns ³∑_u⁺ metastable state of Ar₂ (303 ± 20 cm^-1) and Kr₂ (172 ± 10 cm^-1) were also measured and the vibrational frequencies are consistent with previously reported values. Absorption peaks which are attributed to ns ³∑_u⁺ → m′p ³∑_g⁺ Rydberg transitions of Ar₂ (6≤m′≤10) and Kr₂ (7≤m′≤10) are also reported.