Level energies are reported for Si V, Si VI, Si VII, Si VIII, Si IX, Si X, Si XI and Si XII. The energies have been calculated with the relativistic Multi-Reference Møller-Plesset Perturbation Theory method and include valence and K-vacancy states with up to 5. The accuracy of the calculated level energies is established by comparison with the recommended data listed in the National Institute of Standards and Technology (NIST) on-line database. The average deviation of valence level energies ranges from 0.20 eV in Si V to 0.04 eV in Si XII. For K-vacancy states, the available values recommended in the NIST database are limited to Si XII and Si XIII. The average energy deviation is below 0.3 eV for K-vacancy states. The extensive and accurate dataset presented here greatly augments the amount of available reference level energies. We expect our data to ease the line identification of L-shell ions of Si in celestial sources and laboratory generated plasmas, and to serve as energy references in the absence of more accurate laboratory measurements.

Calculated level energies for valence and K-vacancy states are provided for the ion series S VII - S XIV and Ar IX - Ar XVI. The calculations were performed with the relativistic Multi-Reference Mxller-Plesset Perturbation Theory method (MR-MP). The data set includes all the level energies with configurations 1s22(s, p)q, 1s22(s, p)q−1nl, 1s12(s, p)q+1, 1s12(s, p)qnl, 2(s, p)q+2 and 2(s, p)q+1nl, where 1 ≤ q ≤ 8, n ≤ 5 and l ≤ 3. We have compared our results with data from the National Institute of Standards and Technology (NIST) on-line database and with previous calculations. The average deviation of valence level energies ranges from 0.16 eV in Ne-like ions to 0.01 eV in Li-like ions, showing that the present MR-MP valence level energies are highly accurate. In the case of K-vacancy states, the deviation is generally below 0.3 eV for Li-like S XIV and Ar XVI. The deviation for K-vacancy energies in other L-shell ions (Be-, B-, C-, N- and O-like Ar ions) is higher but likely because the NIST-recommended values have a higher uncertainty. The data set includes many n = 4 and n = 5 valence and K-vacancy levels in L-shell ions of S and Ar not previously reported. The data can be used for line identification and modeling of L-shell ions of S and Ar in astrophysical and laboratory-generated plasmas, and as energy references in the absence of more accurate laboratory measurements.