This study of molecules adsorbed on a solid surface is supported by the NSF Theoretical and Computational Chemistry program. The molecule-phonon interaction is treated quantum mechanically using a Hamiltonian operator that can include multiple phonons, as well as the hindered translational, rotational, and vibrational modes of the molecule, and all possible interactions of these degrees of freedom. Both weak (one phonon) and strong (multi-phonon) interactions can be described. The nature of the trapped state with regard to desorption, relaxation, and hot atom chemistry is treated. The effect of varying the component of beam energy parallel to the surface is also studied. Computer models are used in this research to study the motion of molecules adsorbed on solid surfaces. The goal is to gain fundamental knowledge of the principles of surface chemistry, which in turn relates to chemical processes of great practical importance such as heterogeneous catalysis. Computer modeling is a widely used theoretical tool for the study of such processes. The special role of this research project is to test the validity of various mathematical and physical approximations commonly employed in these computations. In particular, the laws of quantum mechanics, rather than classical mechanics, are applied, and the interaction of the molecule with one or more phonons (quantized lattice vibrations) are treated.
