Abstract

The odd parity levels in SI contain two related major anomalies, a bound (3s)1(3p)5 3P term, with very small oscillator strengths to the (3s)2(3p)4 3P ground-state term. Configuration interaction calculations, with a discretized continuum model, by Cowan, Radziemski, and Kaufman predict a bound (3s)1(3p)5 3P term as a result of its strong interaction with the continuum. It is shown that the discretized continuum model is in error in its treatment of the continuum, and that an exact solution to an approximate model shows that the energy shift due to interaction with the continuum is weak. Hansen has treated the comparable strong perturber problem in the halogens as a two-level interaction problem between (n s)1(n p)6 2S and (n s)2(n p)4 1D (n d)2S, using a term-dependent Hartree-Fock wave function for the latter level. Hansen’s results are in reasonable agreement with the discretized continuum model. It is shown that this agreement is fortuitous, as the two approaches treat different continuum interactions. In addition it is shown that Hansen’s two-level treatment is not generalizable. For SI both (3s)2(3p)3 2D (3d)3P and (3s)2(3p)3 2P (4s)3P must be included in the calculation even though (3s)2(3p)3 2P (4s)3P interacts weakly with (3s)1(3p)5 3P. Discrete CI calculations indicate that one can find reasonable overall agreement with the observed SI odd parity energy levels with J = 1 if the initial energy of the (3s)1(3p)5 3P is treated as a free parameter. Calculated level widths are in reasonable agreement with experiment, indicating no need to rescale calculated nondiagonal matrix elements. The calculated (3s)1(3p)5 3P–(3s)2 (3p)4 3P oscillator strengths are large, in contradiction to experiment. This fact and the need to use an adjustable (3s)1(3p)5 3P initial energy suggests a source of strong CI, not included in the basis set used. It is hypothesized that the missing strong source is the (3s)1(3p)4(4p) configuration.

© 1979 Optical Society of America

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