| 概 要 |
講演１
Prof. Yunjie Xu (Univ. of Alberta, Canada)
"Spectroscopy of chiral molecules: from the gas phase to solution"
Abstract
A series of high resolution spectroscopic studies of small chiral molecular adducts and low resolution infrared multiphoton dissociation studies of protonated serine clusters will be presented. Using the experimentally spectral signatures, complemented with the ab initio calculations, we examine the chiral discriminating forces at play in these molecular systems. I will also discuss our two-pronged approach to study the effects of solvent-solute hydrogen-bonding on chiroptical measurements using both high resolution spectroscopy and vibrational circular dichroism (VCD) spectroscopy. We observed that some vibrational bands of an achiral molecule, such as water, can show significant VCD strength through hydrogen-bonding to a chiral molecule. This effect, termed chirality transfer, will be discussed.
講演２
Prof. Wolfgang Jaeger (Univ. of Alberta, Canada)
"Spectroscopic Studies of Quantum Solvation"
Abstract
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 He_N-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 He_N-CO [3].
Molecular hydrogen, specifically para H_2, 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 para H_2 clusters are believed to be fluid. We have studied (para H_2)_N-molecule clusters to find evidence for superfluid behaviour in the trends of spectroscopic parameters, similar to the case of He_N-molecule clusters. Spectra of paraH2 clusters with OCS, N_2O, 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 ammonia [4] and carbonyl sulphide [5] and infrared studies of hydrogen peroxide will be presented.
[1] J. Tang, Y. Xu, A. R. W. McKellar, and W. Jager, Science 297, 2030 (2002).
[2] A. R. W. McKellar, Y. Xu, and W. Jager, Phys. Rev. Lett. 97, 183401 (2006).
[3] 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).
[4] R. Lehnig and W. Jager, J. Chem. Phys. 127, 241101 (2007).
[5] R. Lehnig, P. L. Raston, and W. Jager, Faraday Discuss. 142, 297 (2009).
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