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

Abstract

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.

Spectroscopic properties of the Ar*2(5p) excimer states

“…This is the reason, why fluorescence from these states has never been reported except for the observation of a faint emission on the Ar * 2 (5p 3 Σ g ) → Ar * 2 (4s 3 Σ u ) 1 transition [11]. On the other hand, complete Rydberg series of Ar * 2 (np 3 Σ g ) and Ar * 2 (np 3 Π g ) triplet states have been found [3][4][5][6][7][8][9] by absorption spectrometry. Of the corresponding singlet states only the Ar * 2 (4s 1 Σ u ) is known due to its decay into the repulsive ground state.…”

“…The excited states of Ar 2 have been studied by absorption spectroscopy starting from the van der Waals ground state [1,2] Ar 2 (3p 6 1 Σ g ) or the excimer state [3][4][5][6][7][8][9] Ar * 2 (4s 3 Σ u ). Bound states result by adding an electron in a nλ configuration to the ionic dimer state Ar + 2 ( 2 Σ u ).…”