CHANNEL INTERFERENCE IN RESONANT AUGER SCATTERING BY SURFACE-ADSORBEDMOLECULES

We present theory of resonant Auger scattering in gas-phase and surfac e-adsorbed molecules focusing on the role of channel interference. The connections between parity selection rules, parity of the Auger elect ron wave functions, Bragg conditions, and channel interference are unc overed. The channel interference is found sensitively dependent on the phase factors of the Auger electron and the incident x-ray photons, s omething that makes the scattering cross sections strongly anisotropic and oscillatory. Parity selection rules are found that apply to a fai rly broad class of molecules, but which can be violated by different d ephasing mechanisms that destroy the coherence. The parity-selection r ules are particularly sensitive to the degree of orientational disorde r of the molecules, something that actually can be used for investigat ions of adsorbate orientation. Three types of coherence destroying, de phasing mechanisms are investigated: orientational disorder, vibration al and librational motion, and scattering of the emitted electron by t he surrounding atoms. It is predicted that the selection rules can be obstructed by thermal vibrations and librations even at very low tempe rature due to the zero-point contributions. The selection rules and th e dephasing mechanisms are explored for one-, two-, and three-dimensio nal adsorbate systems.