Atom-molecule scattering

In crossed beam scattering experiments, the velocity tunability of Stark-decelerated beams offers the revolutionary capability to study (in)elastic or reactive scattering as a function of the continuously variable collision energy, from low to high collision energies, and with a high intrinsic energy resolution. This ability can be exploited, for instance, to accurately measure the quantum threshold behavior of inelastic scattering cross sections.

In 2006, we performed the first scattering experiment using a Stark decelerated molecular beam, using the scattering of OH radicals with Xe atoms as a model system. Read here our publication Near-Threshold Inelastic Collisions Using Molecular Beams with a Tunable Velocity in Science Magazine. During the last few years, we have constructed a new crossed beam scattering apparatus containing the world's largest Stark decelerator.


Crossed-beam scattering machine containing a 2.6 meter long
Stark decelerator

This Stark decelerator enables state-to-state scattering experiments with a sensitivity that exceeds the level of sensitivity that is obtained in state-of-the-art crossed beam scattering experiments of similar systems. We have demonstrated this for the scattering of OH(X 2Π) radicals with rare gas atoms, as well as with D2 molecules.


State-to-state inelastic scattering cross sections for collisions between OH radicals
and Ar atoms. From Scharfenberg et al., PCCP 12, 10660 (2010).

In the measured state-to-state inelastic scattering cross sections, shown above for OH-Ar, the energetic thresholds for scattering into excited rotational levels of OH are clearly recognized. These experiments test quantum chemistry calculations of molecular scattering processes with an extreme level of precision.