Collision-induced desorption of ammonia chemisorbed on Ptˆ111‰: From direct measurement of the threshold energy to determination of the surface–adsorbate bond strength

We report the desorption of a chemisorbed polyatomic adsorbate from a transition metal surface by a beam of neutral, energetic Ar atoms. From direct measurement of the threshold energy for collision-induced desorption we calculate the surface–adsorbate bond energy. The absolute cross sections for NH3 desorption at one-quarter of a monolayer coverage were measured for Ar beam energies up to ;3 eV at incident angles of 0°, 30°, 45°, and 60°. For the NH3/Pt$111% adsorbate– surface system, the threshold desorption energy is found to be 1.9560.17 eV. Using a classical energy transfer mechanism this threshold energy corresponds to a bond energy of 1.160.1 eV using an effective mass of 1 Pt atom. The threshold desorption energy scales with the total energy of the noble gas atoms for each angle of incidence. This result is consistent with a strong lateral corrugation in the NH3/Pt$111% potential energy surface and a similar ejection mechanism at each angle. © 1995 American Institute of Physics.