Lecture by Professor Wolfgang Jager
Spectroscopic Studies of Quantum Solvation
Professor Wolfgang Jager (University of Alberta, Edmonton, AB, Canada)
Room: Collaboration Center 2F 201
Time: May 18th (Wed.) 5:00pm - 5:40pm
High resolution spectroscopy in the microwave and infrared ranges has been applied to study the stepwise solvation of linear molecules with helium atoms. For example, it was possible to measure spectra of HeN-OCS clusters with N close to 100 with atom-by-atom resolution.1,2
These studies have given detailed insight into how superfluidity, formally a bulk phase property, evolves from the microscopic scale. In particular, an increase in rotational constant, B, of the cluster with increasing number of helium atoms N at a certain critical size marks the onset of microscopic superfluidity. Effects of superfluidity have been detected in clusters with as few as four helium atoms in the case of HeN-CO. 3
Molecular hydrogen, specifically paraH2, is the only substance, other than helium, which is suspected to possess a superfluid phase. Experimental verification has thus far been hampered by its relatively high lying freezing point (~14 K), which causes solidification before the transition temperature (< 2 K) is reached. However, small to medium sized paraH2 clusters are believed to be fluid. We have studied (paraH2)N-molecule clusters to find evidence for superfluid behaviour in the trends of spectroscopic parameters, similar to the case of HeN-molecule clusters. Spectra of paraH2 clusters with OCS, N2O, and CO as probe molecules will be discussed.
The second part of the presentation will focus on spectroscopic studies of molecules embedded in helium nanodroplets. These matrix studies yield rotationally resolved spectra, an indicator of the superfluid nature of the helium nanodroplets. Of particular interest are the reduced rotational constants, increased line widths, and shifts in the vibrational band origins, as compared to the gas phase species. Microwave studies of ammonia4 and carbonyl sulphide5 and infrared studies of hydrogen peroxide will be presented.
 J. Tang, Y. Xu, A. R. W. McKellar, and W. Jager, Science 297, 2030 (2002).
 A. R. W. McKellar, Y. Xu, and W. Jager, Phys. Rev. Lett. 97, 183401 (2006).
 L. A. Surin, A. V. Potapov, B. S. Dumesh, S. Schlemmer, Y. Xu, P. L. Raston, and W. Jager. Phys. Rev. Lett. 101, 233401 (2008).
 R. Lehnig and W. Jager, J. Chem. Phys. 127, 241101 (2007).
 R. Lehnig, P. L. Raston, and W. Jager, Faraday Discuss. 142, 297 (2009).
Contact: Prof. K.Kawaguchi