STARK BROADENING PARAMETERS OF ANALOGOUS SPECTRAL LINES ALONG THE LITHIUM AND BERYLLIUM ISOELECTRONIC SEQUENCES

Abstract

We report the results of theoretical and experimental study of the Stark broadening and shifting of analogous spectral lines along the lithium (3 s 2 S–3 p 2 P°) and beryllium (3 s 3 S–3 p 3 P°) isoelectronic sequences. For the evaluation of Stark broadening parameters the impact semiclassical method is used. The Stark widths and shifts along both sequences are measured in the plasma of a low-pressure pulsed arc. Plasma electron densities were determined from the width of the He II P α line while electron temperatures were measured from the relative line intensities. Both experiments agree within estimated uncertainties with our semiclassical results. Although the overall agreement between theory and experiments is found, gradual change of the discrepancy for the widths along the sequence is detected. The comparison of experimental Stark shifts with the theories shows that the magnitude and direction of line shifts along the Li-sequence may not always be predicted by theory. The comparison of experimental Stark widths along the Be-sequence for B II, C III, N IV and O V with semiclassical theory shows a similar tendency. The discrepancy with theory is large for the B II and it is improved for higher members of the sequence. The only measured Stark shifts for N IV and O V are of a different sign (red for N IV and blue for O V), and this change of sign along the sequence cannot be explained by the theory.