Lecture
Van Marum Colloquium: Some observations on atom surface scattering, diffraction and diffusion
- Date
- Monday 2 February 2026
- Time
- Location
-
Gorlaeus Building
Einsteinweg 55
2333 CC Leiden - Room
- CE.0.18
Abstract
Many experiments have been carried out to study atom-surface interactions. A prominent effect, is rainbow scattering of especially heavy atoms on surfaces. A related observation is the measured angular quantum diffraction pattern when considering light atoms, especially Helium. Quantum diffraction has also been observed for heavy atom scattering under special conditions. Quasielastic Helium spin echo atom scattering has been used to determine surface diffusion coefficients as well as hopping rates. A different but complementary group of experiments are known as GIFAD – Grazing Incidence Fast Atom Diffraction – among others, they also reveal rainbows and quantum diffraction patterns.
All these experiments call for theoretical developments. Analytical results in atomic and molecular dynamics are few and far between, yet those that do exist go a long way in explaining phenomena and setting our intuition. Classical and semiclassical perturbation theory plays a major role in extending analytic results to increasingly complex systems. In this talk I will review the classical first and second order theory of rainbow surface scattering, showing that it accounts correctly for the energy dependence of rainbow angles and the angular distance between them as a function of incidence angle and energy. Second order perturbation theory is necessary to account for the asymmetry in rainbow scattering.
The semiclassical theory led to the conclusion that collimation of the incident beam may be used to observe diffraction in heavy atom scattering. This prediction was subsequently verified experimentally and lies at the heart of recent observations of diffraction of He and H atoms when scattered through single-layer graphene.
Classical and semiclassical perturbation theory is useful in the context of GIFAD scattering. It accounts for the diffraction patterns in the GIFAD scattering of the He atom on a LiF surface. We distinguish between GIFAD scattering in a symmetry plane and out of it. In the former case, the scattering reduces to a two dimensional problem, in the latter, it becomes a time dependent two dimensional problem.
The semiclassical theory will be used to account for the role of tunneling in surface diffusion, concentrating on the rates for H and D atom hopping on a Pt(111) surface. Recent results in thermal reaction rate theory, guide our understanding of the differences between H and D atom hopping even when the temperature is not very low.