Interatomic potentials for ground and excited states of Ar+He

The potential energy curves (PECs) of the ground and excited states that correlate in the atomic limit with Ar([Ne]3s ²3p ⁶,¹S), Ar([Ne]3s ²3p ⁵4s ¹, ³P, ¹P), and Ar([Ne]3s ²3p ⁵4p ¹, ³D, ³P, ³S, ¹D, ¹P, ¹S) are calculated at the multireference configuration interaction (MRCI+Q) theoretical level with extrapolations to the complete basis set limit using all-electron correlation consistent triple-, quadruple-, and quintuple-zeta basis sets. Scalar relativistic corrections are calculated using second-order Douglas-Kroll-Hess Hamiltonian with the corresponding basis sets contracted for scalar relativistic Hamiltonians. For these calculations, the 3s orbitals of the Ar atom are not included in the active space but are correlated through single and double excitations. Spin-orbit eigenstates are computed by diagonalizing the Breit-Pauli matrix between internal configurations with no electrons in external orbitals and added to the scalar relativistic results. A total of 32 molecular PECs are computed with spin-orbit contributions, which correlate with 1s₁, 1s_5-2, and 2p_10-1 atomic Ar energies in Paschen notation. Important features of the PECs and system crossings are discussed.