NH3 PHYSISORPTION ON MGO(100) SUBSTRATE - POTENTIAL CALCULATIONS REVISITED

On the basis of new experimental results on the adsorption-desorption-diffusion mechanisms of NH3 on the MgO(100) surface, the adequacy of interaction potentials based on the physisorption hypothesis is discussed. It is shown that the calculated adsorption energy is consistent with the experimental one when the effective charge of the Mg and 0 substrate atoms is equal to 1; this latter value is very close to that determined elsewhere using a self-consistent tight binding method. The calculations interpret the low value for the saturation coverage in terms of repulsive lateral interaction between ammonia molecules. The influence of charge transfer between NH3 and Mg on the behavior of the adsorption energy with the NH3 coverage is also quantitatively estimated.