Spectroscopy of "Large" Molecules on Earth and Elsewhere

Presented by Jens-Uwe Grabow, Hannover University

Larger molecules and molecular clusters are gaining not only technological but also academic attention with numerous questions on their structure and dynamical behaviour as well as fundamental problems in physics waiting to be answered. Targeted by high resolution spectroscopy, they impose a number of challenges, theoretically and experimentally. From the theoretical point of view, e.g., internal large amplitude motions result in complicated energy level schemes. For larger species exhibiting multiple internal motions at low barriers, the resulting spectra will be rather difficult to predict. From an experimental point of view, dense spectra at the presence of wide splitting patterns are difficult to assign. With narrow-banded techniques, even though very sensitive, identification of such spectral features becomes a paramount task. Nevertheless, the unrivalled resolution of these techniques provides a window to tackle fundamental questions in physics - potentially even beyond the standard model. Quantitative information on the structure, charge distribution, characterization of the chemical bond, details on internal dynamics, etc. - at the highest precision available to date - are encoded in pure rotational spectra obtained by microwave spectroscopy. Among others, we will present an example where internal movement is not governed sterically through space but electronically through a conjugated pi-bond system. Right now - about a quarter century after the introduction of supersonic-jet resonator Fourier-transform microwave spectroscopy - new exciting technical developments promise to overcome still existing limitations of rotational spectroscopy. First examples will be presented.