Ab initio studies of the x-ray absorption edge in copper complexes. I. Atomic Cu^{2+} and Cu(ii)Cl_{2}

lower is a group of transitions involving ls 4p simultaneous with ligand-to-metal shakedown. About 18.7 eV below the main peak is a weak (65 times weaker) quadrupole-allowed transition corresponding to 1s 3d (i.e., ls 3d ls'3d' ). These results are in agreement with typical assignments of x-ray absorption spectra of Cu(tt) systems except that the middle transition is usually assigned as 1s 4s, whereas we find this transition to be 1s —4p plus shakedown. (Transitions of the character ls 4s are calculated but have intensities far too low to have been observed. )