On the possibility of using differential cross section measurements for the electronic excitation of adsorbates by an electron beam, to determine the adsorbate orientation

We show, by detailed electron–molecule scattering calculations, that the angular dependence of electron energy loss spectra in which an adsorbate is electronically excited can be used to identify the orientation of the molecule with respect to the surface and the nature of the final states. The calculations are exploratory and were carried out for an H2 molecule. The transition amplitude for electron–molecule scattering is calculated by using the Schwinger variational principle with two open channels. The effects of the surface were introduced through a semiquantitative model which treats the surface as a partly reflecting, flat mirror.