SHORT WAVELENGTH LASER CALCULATIONS IN THE Be I, B I AND C I ISOELECTRONIC SEQUENCES

Abstract
Short Wavelength Laser Calculations in the Beryllium, Boron and Carbon Isoelectronic Sequences - Level populations of the 2s3p, 2s²3p 2 and 2s²2p3p configurations in ions of the Be I, B I and C I isoelectronic 2 sequences can be inverted with respect to populations of the 2s3s, 2s²3s, and 2s²2p3s configurations by electron collisional pumping. In the case of B I and C I ions, the process is analogous to the process for Ne-like ions which has lately received considerable attention. In the case of Be I ions, the inversion is a consequence of the slow radiative decay of the 2s3p ³P₂ and 2s3p ³P₀ levels. Level populations are calculated for Be-like, B-like and C-like ions with atomic number Z between 18 and 36 and for electron densities from 10¹⁵ to 10²² cm^-3. For each of the Be I and B I isoelectronic sequences, 20 levels are involved with principal quantum number n equal either to 2 or 3. For the CI isoelectronic sequence 46 levels are involved. Using the level populations, gain coefficients are calculated for transitions of the type 2s3s - 2s3p, 2s²3s - 2s²3p and 2s²2p3s - 2s²2p3p. The calculated gain coefficients are compared to previous calculations. At high electron densities where collisional mixing of the excited levels becomes important, the intensities of the X-ray transitions from the 2s^k2p^m3p levels decrease relative to the X-ray transitions from the 2s^k2p^m3s and 2s^k2p^m3d levels where k=1, m=0 or k=2, m=0,1. The density dependence of these X-ray line ratios is calculated elsewhere /16, 17/. These line ratios represent a promising diagnostic for electron density. Finally, the opacities of the 2s2p - 2s3s, 2s²2p - 2s²3s and 2s²2p² - 2s²2p3s transitions are discussed for plasma parameters for which a reasonable gain can be achieved.