Roland Wester' s research interests lie in the field of molecular interactions and reaction dynamics. Specifically, ions and ionic clusters are studied using cryogenic ion traps and controlled collision experiments, analyzed by mass spectrometry and three-dimensional momentum imaging. This yields rich information on the atomistic dynamics of the involved molecular groups and allows the identification of characteristic reaction mechanisms. Quantum state-specific dynamics are targeted using low temperatures and state-specific infrared and terahertz excitation. The applications of these methods range from model systems in organic chemistry to cold molecules found in interstellar gas clouds.