Ab initiostudies of the x-ray absorption edge in copper complexes. I. AtomicCu2+and Cu(ii)Cl2

Abstract

As a first step in the study of the structure at x-ray absorption edges, we have examined the discrete transitions corresponding to the atomic $1s\to 3d, 4s, 4p, 5s, \mathrm{and} 5p$ transitions and the corresponding shakeup processes for Cu atom and for a Cu(ii) model system, Cu${\mathrm{Cl}}_2$. For Cu${\mathrm{Cl}}_2$ the lowest strong transitions have the character $1s\to 4p$ ($f=0.001\mathrm{}33$). About 7.5 eV lower is a group of transitions involving $1s\to 4p$ 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 $1s\to 3d$ (i.e., $1s^{2}3d^9\to 1s^{1}3d^{10}$). These results are in agreement with typical assignments of x-ray absorption spectra of Cu(ii) systems except that the middle transition is usually assigned as $1s\to 4s$, whereas we find this transition to be $1s\to 4p$ plus shakedown. (Transitions of the character $1s\to 4s$ are calculated but have intensities far too low to have been observed.)