Infoscience

Journal article

Chemisorption and macroscopic diffusion of NO on Pt(111)

Thermal energy helium scattering is used to measure the isothermal desorption of NO from Pt(111) in the temperature range 343-383 K. Taking into account the vibrational degrees of freedom to calculate the residence time of the molecules, the energy of adsorption is E/sub a/=-29.8+or-1 kcal/mol, and a repulsive interaction energy between molecules is found: phi =6.1+or-1 kcal/mol. Also, the macroscopic diffusion of NO on Pt(111) is measured for the first time between 313 and 358 K. The technique uses a helium beam to monitor the time dependence of the coverage on a well defined surface spot, when the adsorbed molecules diffuse outside this spot. The activation energy for diffusion at low coverage is E/sub D/=11.8+or-1.2 kcal/mol, and the pre-exponential factor is D/sub 0/=2.4*10/sup -3/ m/sup 2//s.

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