Thermal energy He scattering was used to measure the isothermal desorption of NO from Pt(111) at temperatures ranging from 343 to 383K. By taking account of vibrational degrees of freedom in order to calculate the residence time of the molecules, the energy of adsorption was estimated to be -29.8kcal/mol, while the repulsive interaction between molecules was 6.1kcal/mol. Also, the macroscopic diffusion of NO on Pt(111) was measured for the first time at temperatures between 313 and 358K. The technique involved the use of a He beam to monitor the time dependence of the coverage at a well-defined surface spot, as the adsorbed molecules diffused out of this spot. At low coverages, the NO diffusivity (table 18) could be described by:

D (m2/s) = 0.0024 exp[-11.8(kcal/mol)/RT]

M.Croci, C.Félix, G.Vandoni, W.Harbich, R.Monot: Surface Science, 1994, 307-309, 460-4

Table 18

Diffusion of NO on (111)Pt Surfaces