The relative intensities of hydrogen-like fine structure

Abstract

The ratio of the intensities of the Lyman alpha (n=2 to 1), Balmer alpha (n=3 to 2) and Balmer beta (n=4 to 2) fine structure components of hydrogen-like ions emitted from plasmas of various atomic number Z is examined. The fine structure intensities of Lyman alpha can only be deduced assuming statistical equilibrium between the fine structure sub-levels of quantum state n=2 for electron densities Ne>or approximately=1013Z9 cm-3, while the fine structure intensities of Balmer alpha and beta can only be deduced assuming statistical equilibrium between the sub-levels of n=3 and 4 respectively for Ne>or approximately=1012Z9 cm-3. At low electron densities (Ne<or approximately=103Z9 cm-3 for Lyman alpha, Ne<or approximately=107Z9 cm-3 for Balmer alpha and beta), the fine structure intensities are given by a coronal-like model, where collisional processes into the sub-levels are balanced by radiative de-excitation. At intermediate electron densities, the Lyman alpha, Balmer alpha and Balmer beta fine structure ratios can vary rapidly with Ne and should be useful as electron density diagnostics.