A new high-resolution study of the 3d-subshell excitation spectrum of chromium

The authors report new high-resolution 3d-photoabsorption spectra of Cr I. The object of the study was to provide further insight into the remarkable simplicity of the previously studied 3d-excitation spectra of Cr I and Mn I by making observations at much greater resolution. The authors have resolved all the K components of the lines predicted by JK coupling, but not the full multiplicity. In addition, all autoionisation widths and interchannel interactions are found to be very small. These properties of the spectra can be accounted for by the hydrogenicity of the excited np orbitals, which is shown to underpin the spectator-electrons approximation. The authors are also able to justify the hydrogenicity of the np wavefunctions by comparison with species adjacent to chromium in the periodic table.