Classification of iron VIII to XII and XIV lines in the solar extreme ultra-violet spectrum and their isoelectronic sequences from argon to nickel

Abstract

Many of the stronger members of the group of solar emission lines between 167 A and 220 A have been classified as transitions of the type 3pn-3pn-13d in Fe IX to Fe XIV and 3p63d-3p53d2 in Fe VIII. The method is based upon following the isoelectronic sequences from nickel down, where possible, to known spectra. The sources used include Zeta and vacuum sparks. It was necessary to take account in several cases of the interaction between 3d and 4s orbitals at some point in the sequence. Failure to do so in the past has led to wrong classification of lines from 3pn4s terms in the literature. New wavelengths are given for several sequences from argon or potassium to nickel, and many of the new nickel lines can also be found in the solar spectrum between 144 A and 165 A.