Dynamics Of Adsorption And Desorption Of Deuterium Molecules On Ag(Ⅲ) Single Crystal Surface

A value of energy barriers to dissociative adsorption on a single crystal surface is a very important dynamical parameter. There are two approaches to investigate the adsorption energy barriers. One approach is to measure adsorption probability as a function of the kinetic energy of incident molecular beam using the molecular beam scattering technique. However, we cannot obtain information on adsorption barriers directly from the adsorption data. The other approach is to measure the kinetic energy distribution of molecules desorbing from a single crystal surface; and based on analyzing the energy released during desorption, information on the adsorption energy barriers can be obtained. This thesis employed the second approach.In this thesis, a new model was described for calculation of the kinetic energy distributions of molecule desorbing from a single crystal. Using the model, we have studied the experimental kinetic energy distribution of deuterium molecules (D₂) recombinatively desorbing from the Ag(111) single crystal surface. At the surface temperature of 295K, there are two peaks on the energy distribution of D₂ desorbing from Ag(111). The first peak can be fitted by a Maxwell-Bolzmann distribution. We suggest that the desorption sites of molecules which correspond to the first peak should be located at defects and steps of the surface, which have adsorption barrier heights close to zero. The second peak is located at 75meV. Based on results of the model calculations, we suggest that the desorption sites of molecule corresponding to the second peak should be between terraces and defects (or steps) of a surface. The terrace of a single surface has a higher adsorption energy barrier than defects and steps of the surface.At the surface temperature of 570K, there is a high energy peak besides the low energy peaks. The high energy peak of molecules desorbing into the vibration ground state(v=0) and desorbing into the vibration excited state is located at 1.1eV and 0.8eV, respectively. The high energy peak can be attributed to the desorption of D₂ molecules from the sub-surface sites of Ag(111).