Research Group Prof. Dr. G. Friedrichs

PCCP Poster Prize 2017: Molecular Orientation Effects Uncovered

PCCPosterPrize201727 May 2017 


Ann-Katrin Baumann returned with a PCCP poster prize from the 116th General Assembly of the German Bunsen Society for Physical Chemistry in Kaiserslautern. Congratulations! Her poster "Sub-Monolayer NIR-ew-CRD Spectroscopy: Picosecond Versus Continuous Wave Laser Excitation“, which has been presented in the session "Experimental Techniques", has been selected from over 230 poster contributions.The presented results from Ann-Katrin's Master thesis was a follow-up of the dissertation of Inga Piller. In contrast to Inga, who used a continuous wave laser as a light source for her evanescent-wave cavity ringdown experiment, the new measurements were performed with a pulsed picosecond laser. It turns out that the performance of the spectrometer, which is used to investigate organic molecules adsorbed at a quartz surface, was improved allowing us to detect 1/10th of a monolayer of TCE (trichloroethylene). Moreover, polarization dependent measurements revealed an overall orientation of the molecules at the interface with TCE lying essentially flat on the surface. Interestingly, the TCE molecules even keep this preferred orientation for surface coverages corresponding to several monolayers thickness. This fascinating result will be further investigated in future experiments using sum-frequency generation spectroscopy and molecular dynamics simulations. In principle, it should also be possible to further enhance the performace of the spectrometer to <1/100th monolayer coverage detection sensitivity by simply using a laser with higher repetition rate. Such a spectrometer would offer us a versatile tool to study structural effects as well as to investigate the reactivity of organic monolayers.