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 symmet ric electronic states of adsorbates. The origin of this new class of C DAD effects is electron reflection. A simple reflection mechanism incl uding inelastic processes is introduced into the theory of the angular -resolved photoemission from adsorbates excited by polarised light. Th is model is expanded by including electron diffraction. Both models sh ow that interference of partial waves of the same orbital quantum numb er causes CDAD for spherical initial states of adsorbed atoms. The int erference is due to the difference in the path length of the direct an d the reflected wave and in the case of diffraction additionally to th e scattering phase shift. The CDAD derived theoretically is in agreeme nt with experiments with free laser aligned and adsorbed alkali atoms.