THE SOLID-SURFACE AS ORIGIN OF CIRCULAR-DICHROISM IN THE ANGULAR-DISTRIBUTION OF PHOTOELECTRONS FROM SPHERICAL STATES OF ADSORBATES

It is shown that the presence of the surface causes circular dichroic effects in angular-resolved photoemission (CDAD) from spherical symmetric electronic states of adsorbates. The origin of this new class of CDAD effects is electron reflection. A simple reflection mechanism including inelastic processes is introduced into the theory of the angular-resolved photoemission from adsorbates excited by polarised light. This model is expanded by including electron diffraction. Both models show that interference of partial waves of the same orbital quantum number causes CDAD for spherical initial states of adsorbed atoms. The interference is due to the difference in the path length of the direct and the reflected wave and in the case of diffraction additionally to the scattering phase shift. The CDAD derived theoretically is in agreement with experiments with free laser aligned and adsorbed alkali atoms.