講演会のお知らせ （2/21： Prof. J.M. Doyle, Department of Physics, Harvard University）
2014年01月22日
極限量子研究コア・量子宇宙研究センター合同セミナー開催のお知らせ
Harvard大学物理学科のJ. M. Doyle教授をお招きし，セミナーを開催いたします．Doyle教授は，レーザー冷却の困難な分子をHeバッファガスで冷却し，極低温・高輝度の分子ビームを生成する方法の第一人者です．ごく最近，この極低温分子技術を応用し，キラル分子を識別する新しい回転分光手法の開発に成功し[1,2]，キラル分子の分光学的研究において注目を集めるとともに今後の急速な展開が期待されています．また，極低温分子を使った別の研究として，電子EDM探索において従来の上限値 (world record) を一桁以上下げる結果を得る[3]など，基礎物理から化学に至る幅広い分野で成果を上げ注目されています．
今回はこれら最新の研究成果のうち，キラル分子の分光学的識別手法に焦点を絞ってご講演いただきます．
講演リーフレット
“Cold, Large Molecules: Chirality, Trace Detection and Sticking”
日 時： 2014年2月21日（ 金）14：00～15：30
会 場： 岡山大学理学部１階 小会議室
講 師： Prof. J.M. Doyle, Department of Physics, Harvard University
概 要：
We are studying polyatomic molecules in an experimental apparatus that can provide large collision rates under constant, low energy controlled conditions. This has been made possible through the advent of a novel cooling method that allows the introduction of hot polyatomic molecules into a cryogenically cooled, low density inert gas.
As part of these studies we have developed methods for trace detection of molecules in mixtures, in both the optical and microwave regime. The cooling of the molecules leads to dramatic increase in the inverse of the internal molecular ro-vibrational partition function. For example, cooling of anthracene (C14H10) from 300K to 4K would lead to more than a ten order of magnitude increase in the per quantum state phase space density of the molecular ensemble.
In addition to species identification, we have also demonstrated a method to measure the absolute chirality of the molecular species, and enantiomeric excess. Chirality plays a fundamental role in the activity of many biological molecules and in broad classes of chemical reactions. Spectroscopic methods for determining enantiomeric excess include optical circular birefringence (CB), circular dichroism (CD), vibrational circular dichroism (VCD), and Raman optical activity (ROA). All of these chiral analysis methods yield zero signal in the electric-dipole approximation. In contrast, the electric-dipole signal from sum-frequency generation can be non-zero in a bulk chiral environment. Sum-frequency generation (SFG) in the infrared and visible has been observed in samples of chiral molecules in solution in previous experiments. Doubly resonant SFG in both the infrared and microwave regime has been proposed but not observed. We recently demonstrated enantiomer-sensitive spectroscopy by combining a resonant microwave field with a strong adiabatically switched orthogonal non-resonant (DC) electric field.
Following on that previous work, and using our novel cooling method, we demonstrated true sum-frequency generation, a type of three-wave mixing, on a chiral sample in the microwave regime. We use two orthogonally polarized resonant applied electric fields to induce a third mutually orthogonal field at their sum frequency. The phase of this induced field changes sign with enantiomer, and its amplitude provides a sensitive, quantitative measure of enantiomeric excess. The narrow rotational resonances used make this measure of enantiomeric excess fundamentally mixture compatible: in contrast to other spectroscopic methods, the measurement of E.E. of a given species will not be confused by other chiral or non-chiral mixture components in the sample.
I will discuss this new chiral detection method, our efforts on trace detection, and if time permits, our progress on answering the question of sticking of single atoms to large molecules at low temperatures.
参考文献
[1] "Enantiomer-specific detection of chiral molecules via microwave
spectroscopy", D. Patterson, M. Schnell, and J. M. Doyle
Nature 497, 475 (2013)
http://www.nature.com/nature/journal/v497/n7450/full/nature12150.html
[2] "Sensitive Chiral Analysis via Microwave Three-wave Mixing",
D. Patterson and J. M. Doyle, Phys. Rev. Lett. 111, 023008 (2013)
http://prl.aps.org/abstract/PRL/v111/i2/e023008
[3] "Order of Magnitude Smaller Limit on the Electric Dipole Moment
of the Electron", The ACME Collaboration, Science 343, 269 (2014)
http://www.sciencemag.org/content/343/6168/269.abstract
問い合わせ先：理学部附属量子宇宙研究センター 植竹(内線7909)