The momentum vectors for CO in ESD. (Left) The drawing shows the location of the terminally bonded CO molecule on its atop Cu site on Cu(110). (Right) The drawing shows the resultant vectors, pd1 and pd2, for desorbing CO with two selected normal momenta, pz1 and pz2. It is assumed that the lateral momentum, px, is conserved upon excitation by electron impact (8, 9). The distance dprm is parametized in the analysis leading to Fig. 9. [Reprinted with permission from refs. 8 and 9 (Copyright 1987, American Institute of Physics.)]