Calculations of Energy Levels of the Singly Excited States (1snl) 1,3Lp for Heliumlike Ions with Z ≤ 12

In this paper we present accurate calculated data of the energy levels of the 1snl1,3Lp states (l = s, p, d; n = 2 – 10) of helium and heliumlike ions up to Z = 12 using the variational approach of the Screening Constant by Unit Nuclear Charge (SCUNC) formalism. These calculations are performed by solving the time-independent Schrödinger equation using a new explicitly correlated wave function. A thorough comparison with theoretical predictions available in the literature for the energy levels of the singly excited 1sns1,3Se, 1snp1,3P0and 1snd1,3De Rydberg series is performed. Most of the tabulated results are generally in good agreement with the available reference data, confirming the reliability of our results. SCUNC predictions up to n = 10 may provide reliable atomic data for related experiments in the future.