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 Title: Molecular chirality: enantiomer differentiation by high-resolution spectroscopy Author(s): Hirota, Eizi Subject(s): Structure determination Abstract: I have demonstrated that triple resonance performed on a three-rotational-level system of a chiral molecule of C$_{1}$ symmetry exhibits signals opposite in phase for different enantiomers, thereby making enantiomer differentiation possible by microwave spectroscopy\footnote{E. Hirota, 3rd Molecular Science Symposium, Nagoya, September 2009, E. Hirota, Proc. Jpn. Acad. Ser. B, 88, 120 (2012).}. This prediction was realized by Patterson et al. on 1,2-propanediol and 1,3-butanediol\footnote{D. Patterson, M. Schnell and J. M. Doyle, Nature 497, 475 (2013), D. Patterson and J. M. Doyle, Phys. Rev. Lett. 111, 023008 (2013).}. We thus now add a powerful method: microwave spectroscopy to the study of chiral molecules, for which hitherto only the measurement of optical rotation has been employed. Although microwave spectroscopy is applied to molecules in the gaseous phase, it is unprecedentedly superior to the traditional method: polarimeter in resolution, accuracy, sensitivity, and so on, and I anticipate a new fascinating research area to be opened in the field of molecular chirality. More versatile and efficient systems should be invented and developed for microwave spectroscopy, in order to cope well with new applications expected for this method For C$_{2}$ and C$_{n}$ (n $\geq$ 3)chiral molecules, the three-rotational-level systems treated above for C$_{1}$ molecules are no more available within one vibronic state. It should, however, be pointed out that, if we take into account an excited vibronic state in addition to the ground state, for example, we may encounter many three-level systems. Namely, either one rotational transition in the ground state is combined with two vibronic transitions, or such a rotational transition in an excited state may be connected through two vibronic transitions to a rotational level in the ground state manifold. The racemization obviously plays a crucial role in the study of molecular chirality. However, like many other terms employed in chemistry, this important process has been “defined” only in a vague way, in other words, it includes many kinds of processes, which are not well classified on a molecular basis. I shall mention an attempt to obviate these shortcomings in the definition of racemization and also to clarify the implicit assumptions made in Hund’s paradox\footnote{F. Hund, Z. Phys. 43, 805 (1927).}. Issue Date: 2014-06-17 Publisher: International Symposium on Molecular Spectroscopy Citation Info: Hirota, E. MOLECULAR CHIRALITY: ENANTIOMER DIFFERENTIATION BY HIGH-RESOLUTION SPECTROSCOPY. Proceedings of the International Symposium on Molecular Spectroscopy, Urbana, IL, June 16-21, 2014. DOI: 10.15278/isms.2014.TE10 Genre: Conference Paper / Presentation Type: Text Language: English URI: http://hdl.handle.net/2142/55860 DOI: https://doi.org/10.15278/isms.2014.TE10 Rights Information: Copyright 2014 by the authors. Licensed under a Creative Commons Attribution 4.0 International License. http://creativecommons.org/licenses/by/4.0/ Date Available in IDEALS: 2014-11-212015-04-14
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