Observation of n s 3Σ+u(1u, 0−u)→m p 3Πg Rydberg transitions of Ar2 (n=4; 5≤m≤15) and Kr2(n=5; 6≤m≤16) in absorption

Rydberg series of Ar2 and Kr2 have been observed in the visible and ultraviolet (350≤λ≤560 nm) absorption spectra of the lowest-lying metastable states of the dimer (ns 3Σ+u(1u, 0−u); Ar: n=4, Kr: n=5). The most prominent series for Ar2 and Kr2 are assigned to ns 3Σ+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 A2Σ+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 A2 Σ+u ion core. Binding energies of the lowest observed 3Πg 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 Ar2 and Kr2 series (1.656±0.006 and 2.621±0.004, respectively) and ωe−2ωexe for the ns 3Σ+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 3Σ+u→m′p 3Σ+g Rydberg transitions of Ar2 (6≤m′≤10) and Kr2 (7≤m′≤10) are also reported.