COLLISION-INDUCED DESORPTION OF N-2 FROM RU(001)

The dynamics of collision-induced desorption (CID) of N-2 from Ru(001) exposed to hyperthermal rare gas colliders generated in a supersonic atomic beam source have been studied. Low coverage of 0.01 ML N-15(2) at crystal temperature of 96 K was chosen to represent a CID process o f a practically isolated molecule, neglecting the effect of lateral N- 2-N-2 interactions. The cross sections for CID of nitrogen molecules, sigma(des)(E-i, theta(i)), as a function of the kinetic energy and ang le of incidence of Ar and Kr colliders have been measured. It was foun d that sigma(des)(E-i, theta(i)=0 degrees) changes monotonically in th e range 0-25 Angstrom(2) for beam energy in the range of 0.5-5.5 eV an d is insensitive to the type of collider (Ar, Kr) as well as to the ad sorbate isotope (N-14(2), N-15(2)). The threshold energy for desorptio n has been determined to be 0.50+/-0.10 eV, which is twice the binding energy of N-2 to Ru(001). The cross section for CID at a fixed collid er's energy rises approximately four times as the incidence angle thet a(i) increases from 0 degrees to 70 degrees relative to the surface no rmal. Neither normal nor total energy scaling of the cross section cou ld describe the results. The sigma(des)(theta(i)) scales reasonably we ll, however, with the tangential energy of the collider for angles abo ve 30 degrees. Classical molecular dynamics simulations were performed to gain better understanding of the CID process. Threshold energy and angular dependence of the cross section were reproduced very well. Th e predominant CID mechanism was concluded to originate from a direct r are gas-nitrogen collision, in which impulsive-bending and the motion along the surface are coupled to the adsorbate motion which leads to d esorption. (C) 1998 American Institute of Physics. [S0021-9606(98)0102 0-4].