Quadrupolar Transitions Evidenced by Resonant Auger Spectroscopy

From absorption spectra, the only way to bring to the fore the occurrence of quadrupolar transitions is to study their angular dependence. Resonant spectroscopies offer a new opportunity to obtain more insight into excited electronic states by studying lineshape and intensity of decay processes. We show here that resonantly excited Ti ${\mathrm{KL}}_{2,3}{L}_{2,3}$ Auger spectra of ${\mathrm{TiO}}_2\left(110\right)$ carry a clear signature of quadrupolar transitions to localized $e_g$ and $t_{2g}$ $d$-like states, giving access to a direct measurement of crystal field splitting.