Observation and Mechanism of Collision-Induced Desorption: CH4on Ni(111)

The desorption of C${\mathrm{H}}_4$ physisorbed on Ni(111) is observed to be induced by collision with Ar atoms incident with energies less than 2 eV. The absolute cross section for collision-induced desorption is measured as a function of the kinetic energy and incident angle of the Ar beam. The mechanism for desorption is shown to involve a direct and impulsive, bimolecular collision between Ar and C${\mathrm{H}}_4$. Molecular-dynamics simulations show that the energy and incident-angle dependence of the desorption cross section are the consequence of two competing dynamical effects.