The Department of Chemistry, Wayne State University, Detroit, Michigan 48202
Abstract
Direct measurement of the threshold desorption energy for collision-induced desorption is used to determine a chemisorption bond energy. In this experiment the absolute cross section for desorption is measured using x-ray photoelectron spectroscopy as a function of the impact energy between a translationally energetic Ar atom and an ammonia molecule chemisorbed to a Pt{111} single crystal. For this adsorbate-surface system the threshold desorption energy is found to be 1.8±0.17 eV and is independent of the angle of incidence of the Ar beam. Using a classical energy transfer mechanism this threshold energy is found to correspond to a bond energy of 1.4±0.13 eV. This represents an upper limit for the bond strength assuming maximum energy transfer between Ar and NH3 and no internal excitation of the adsorbate at the desorption threshold. ©1994 American Institute of Physics.