ИСТИНА

High-level theoretical estimations of radiative properties for the alkali metal - rare gas pairs are necessary for achieving the predicted high-power (up to several MWatts) continuous-wave operation regime for the gas-phase diode-pumped alkali lasers (DPALs, [1]). The present work reports an ab initio study of energetic and radiative properties of low-lying electronic states of the RbAr excimer using the Fock space coupled cluster method (FSCC). Electronic structure modeling is combined with the evaluation of the non-diagonal matrix elements of the electronic dipole moment operator by the finite-field technique [2]. The effects of relativity are introduced through replacing the inner electronic shells of the Rb atom by the accurate shape-consistent two-component relativistic pseudopotential [3], while nine electrons (4s2 4p6 nl1) are treated explicitly. Spatial parts of the molecular (pseudo) spinors are expanded in the basis of Gaussian functions. The Rb basis set is optimized to provide a balanced description of correlations for the ground and excited states. For Ar the all-electron quadruple-zeta set with additional diffuse functions is used. The set of molecular spinors is obtained by the relativistic Hartree-Fock method for the unperturbed RbAr+ system. Nine electrons of Rb and eight valence electrons of Ar are correlated by the FSCC method with singles and doubles (FSCCSD). The model space is spanned by the configurations with a single electron on one of the lowest-energy virtual spinors of RbAr+. The transition dipole moments (TDMs) between the ground (X2Σ+_{1/2}) and first excited (A2Π_{1/2, 3/2}; B2Σ_{1/2}) electronic states of RbAr are derived from the dependencies of the eigenvectors of the FSCC effective Hamiltonian on the strength of the applied external uniform electric field; on this stage, the same (field-free) model space is used for all field strength values. At the dissociation limit the deviation of the obtained transition probabilities from the experimental ones does not exceed 2%. The TDMs and corresponding potentials will be applied for simulating the absorption spectrum of the Rb vapor in the Ar atmosphere near the 5s-5p transition lines of Rb. The FSCC calculations are performed with the DIRAC15.0 package [4]. The work is supported by the RFBR under Grant No. 16-03-00766. References [1] W.F. Krupke, R.J. Beach, et al., Proc. SPIE 5448, 7, 2004. [2] A. Zaitsevskii, A.P. Pychtchev, Eur. Phys. J. D 4, 303, 1998. [3] N.S. Mosyagin, A.V. Zaitsevskii, A.V. Titov, Int. Rev. At. Mol. Phys. 1, 63, 2010. [4] R. Bast, T. Saue, L. Visscher, et al., DIRAC15, a relativistic ab initio electronic structure program, 2015.