Variation of the C (KVV) Auger angular distribution in the [formula omitted]-resonance of CO

Abstract

We report on angle-resolved high-resolution measurements of C (KVV) Auger spectra of CO in the vicinity of the C (1 s) σ ∗ -shape resonance above threshold. These spectra show clear evidence for the theoretically predicted anisotropic K-shell Auger emission in molecules. Complementary results from angle-resolved photoion-spectroscopy show that the small size of the observed effect is, besides the varying intrinsic anisotropy of the Auger decay, also due to a smaller anisotropy in the primary absorption process than originally predicted but in good agreement with more recent calculations. Contrary to this, some satellite Auger transitions show large anisotropies outside the shape resonance, an effect attributed to a conjugate shakeup transition in the primary photoionization process. All Auger anisotropies show a clear and distinct variation across the shape resonance which enables a distinction between different types of Auger transitions concerning the primary photoionization process.