The effect of inner-shell electrons on the ground and low-lying excited states of KLi: Ab initio study with all-electron basis sets

- Role of inner-shell electrons of KLi on spectroscopic parameters.
- Effects of different active spaces are investigated with all-electron basis sets.
- The ro-vibrational energy levels of the X1Σ+, A1Σ+, 13Σ+, 23Σ+ states are obtained.
- The analytical potential energy functions for the states are proposed.

The potential energy curves (PECs) have been calculated for the X1Σ+, A1Σ+, 13Σ+, 23Σ+ states of KLi using multireference configuration interaction method and large all-electron basis sets. The calculations take into account the effect of inner-shell electrons with different active spaces. The rotational and vibrational energy levels are obtained by solving the Schrödinger equation of nuclear motion based on the PECs. The spectroscopic parameters are determined from the rotational and vibrational levels and compared with the theoretical and experimental reports in the literature. The PECs are fitted into analytical potential energy functions using the Morse long-range potential function. The effect of inner-shell electrons on the PECs, rotational and vibrational energy levels and spectroscopic parameters is analyzed.