title: Rotational dynamics of Li+ions encapsulated in C60cages at low temperatures.
abstract: Li+ions encapsulated in fullerene C60cages (Li+@C60) are expected to be suitable as molecular switches that respond to local electric fields. In this study, the rotational dynamics of Li+ions in C60cages at low temperatures are experimentally revealed for the first time using terahertz absorption spectroscopy. In crystalline [Li+@C60](PF6-), the Li+ion rotates in the carbon cage even at 150 K. The rotational mode gradually changes into a librational mode below 120 K, which is associated with the localization of Li+ions due to the electrostatic interactions with its screening image charge on the C60cage as well as with the neighboring Li+@C60and PF6-ions. A simple rotational/librational energy scheme for the Li+ions successfully explains the spectroscopic results, and the potential of Li+@C60as a molecular switch is discussed based on the energy scheme.
authors.affiliation: Research Center for Structural Thermodynamics, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan. h_suzuki@chem.sci.osaka-u.ac.jp.
authors.forename: Hal
authors.initials: H
authors.lastname: Suzuki
authors.affiliation: Terahertz Sensing and Imaging Research Team, Center for Advanced Photonics, RIKEN, Sendai, Miyagi 980-0845, Japan.
authors.forename: Misaki
authors.initials: M
authors.lastname: Ishida
authors.affiliation: Terahertz Sensing and Imaging Research Team, Center for Advanced Photonics, RIKEN, Sendai, Miyagi 980-0845, Japan.
authors.forename: Masatsugu
authors.initials: M
authors.lastname: Yamashita
authors.affiliation: Terahertz Sensing and Imaging Research Team, Center for Advanced Photonics, RIKEN, Sendai, Miyagi 980-0845, Japan.
authors.forename: Chiko
authors.initials: C
authors.lastname: Otani
authors.affiliation: Idea International Co. Ltd, Sendai, Miyagi 980-8579, Japan.
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Kawachi
authors.affiliation: Idea International Co. Ltd, Sendai, Miyagi 980-8579, Japan.
authors.forename: Yasuhiko
authors.initials: Y
authors.lastname: Kasama
authors.affiliation: Research and Analytical Center for Giant Molecules, Graduate School of Science, Tohoku University, Sendai, Miyagi 980-8578, Japan.
authors.forename: Eunsang
authors.initials: E
authors.lastname: Kwon