The calculation of energy levels for atoms in configurations ls22s22pqnl

Abstract

Reactance matrices for electron collisions with ions in configurations ls²2s²2p⁹(q= 1 to 5), calculated by Saraph, Seaton & Shemming (1969), have been fitted to analytic functions of the energy and extrapolated to energies which give bound states with configurations ls²2s²2p^q(S_iL_i)nlSL. The positions of the bound states are calculated using methods of many-channel quantum defect theory. Allowance can be made for the fine-structure energy of the ion core, by using a representation (S_iL_iJ_i) or a pair-coupling representation (S_iL_i)nlj,J. The calculated level positions are compared with positions determined experimentally. The most detailed results are for the np levels, but some results are given for nsand ndlevels. Some semi-empirical adjustments are made in the calculated matrices, so as to obtain improved agreement between observed and calculated levels. In many cases the most serious source of error in the calculations is the neglect of interactions between configurations 2s²2p^qnland 2s2p^q+1n'l'. For the more highly ionized systems these interactions give rise to perturbed series. A discussion of results for valence-electron states in the neutral atoms, C_I, N_I, O_I, F_Iand N_eIis followed by a discussion of the various iso-electronic sequences. The results enable us: (i) To assess the accuracy of the calculated reactance matrices. (ii) To make identifications. In most cases, but not all cases, the assignments obtained for parentage, and for pair-coupling quantum numbers, agree with assignments which have been suggested previously. In some cases it is found that large admixtures of states occur and that no meaningful assignments of parentage or pair-coupling quantum numbers can be made. (iii) To make predictions. Calculated positions of energy levels, and error estimates, are given for some levels which have not been observed.