Abstract
The L1 XPS spectra of the elements Ar(Z=18) to Kr(Z=36) are calculated from first principles by many-body theory. The energy shift of a L1 level from the relativistic Delta SCF energy is interpreted in terms of a dipole relaxation shift due to L1-L23M45 epsilon f Coster-Kronig processes. For the L1 linewidths of the elements Ar to Kr, the present many-body calculations show a remarkable improvement and give good agreement with the experiment. The drop of the L1 linewidths at Ni(Z=28) is interpreted as due to the quasi-atomic behaviour of the Coster-Kronig processes.