Ab-initio calculations of excited rare gas alkali ions

Abstract

Abstract. The excimer-like ions formed by combining a rare gas ion with an alkali atom were investigated by an ab initio HF-CI calculation. The resulting four bound excited states 1S+, JII, 322+ and 3H were subjected to a semiempirical spin orbit (SO)-coupling yielding eight fine structure levels with angular momenta 12=2, 1 (3) and 0(4). For (NeLi) +, (NeNa) +, (ArLi) +, (arNa) ÷, (ARK) ÷ and (KrLi) ÷ the wavelengths for the five allowed transitions to the ground state were calculated. The results are in close agreement with the experimental results. Also other spectroscopic properties as binding energies, transition moments and vibrational quanta are given. PACS: 31.20.EjDiatomic ions Rg+A formed by combining a rare gas ion (Rg +) with an alkali atom (A) are of great interest, since they decay radiatively into the weakly bound ground state Rg A + formed by an alkali ion and a rare gas atom. In recent experimental investigations [1,2,3,4] it was shown that the ions decay by emission of radiation in the vacuum ultra violet region. Because of the weak bonding of the ground state these ions behave excimer-like and are potential candidates for lasers in the VUV.The observed transitions from the Rg+A ions with Rg = Ar, Kr or Xe and A = Li, Na, K, Rb, or Cs showed a fine structure [3]. In order to clarify its origin, in the present investigation the binding properties of some Rg + A ions were studied by ab-initio calculations.The binding of the Rg + A ions results from the polarizing action of the Rg + ion on the alkali atom. In most cases the asymptotic states Rg + (2P3/2, ZP1/2) + A (2S1/2) form the first excited states of the (Rg + A)* system. In a close vicinity the states Rg (3P0,1, 2, 1P1 )+ A (1S 0) + states are located. The resulting bound states of the molecular ions have 1'32; or 1'3H character leading to a total of eight fine structure levels with angular momenta of f2 = 2(1), 1(3), 0-(2) and 0+(2).Conceptually, the problem has been investigated in several steps. As a starting point serves a Hartree-Fock selfconsistent field (HF-SCF) method based on the assumption that each electron moves in an effective field provided by the nuclei and the whole electron distribution. An improvement to the energy due to non-dynamical correlation effects, which account for the degeneracy between different configurations and a rearrangement of electrons in partially filled shells, has been achieved by adding extra configurations to the HF reference state.