Theoretical Modeling of Sr(^q+) He (q = 0, 1, 2) van der Waals Systems Including Spin-Orbit Coupling

Using an ab initio methodology that incorporates pseudopotential technique in conjunction with pair potential approaches, core polarization potentials (CPP), large basis sets of Gaussian type, and full configuration interaction calculations, we investigate interaction of neutral and charged Sr^q+(q = 0,1,2) with helium atom. In this context, the core-core interaction of Sr²⁺-He is included using an accurately performed potential for the ground state at CCSD(T) level of calculation. Also, the potential energy curves and permanent and transition dipole moments of the ground state and numerous excited states have been performed respectively for Sr⁺He and SrHe systems. Subsequently, the spin-orbit effect is considered by utilizing a semiempirical method for states dissociating into Sr⁺(5p) + He, Sr⁺(6p) + He, Sr⁺(4d) + He, Sr⁺(5d) + He, Sr(5s5p) + He, and Sr(5s4d) + He. The spectroscopic constants of the Sr^q+(q = 0, 1, 2) He states, with and without spin-orbit interaction, are derived and assessed in comparison to the existing theoretical and experimental studies. Such comparison has revealed good agreement, especially, for the Sr⁺He ionic system. Additionally, the spin-orbit effect is considered for the X²Σ⁺ → 2²Π_1/2,3/2 and X²Σ⁺ → 3²Σ_1/2 ⁺ transition dipole moments for Sr⁺He.