Libration (spectroscopy)
Libration (from the Latin verb librare "keep in balance" or "swing"; cf. libra "scales") is a form of to-and-fro movement, also known as a tumbling movement, in which an object with an almost fixed orientation repeatedly moves rotates slightly back and forth. In physics and chemistry , a molecule (or another group of atoms ) can be subject to libration if it is subject to external forces or restrictions that restrict its orientation.
For example, in liquid water (H 2 O), a certain water molecule is attracted to neighboring molecules so that it is given a preferred orientation and cannot rotate freely. (Of course, the neighboring molecules move in the course of time and the preferred orientation changes.) However, it can go through librational movements that can be evaluated in an infrared spectrum and contribute to the movement of other vibrations, such as the OH stretching vibration .
Another example is a molecular crystal: each molecular unit has a preferred orientation due to interactions with neighboring molecules, but they still have libration modes that correspond to small rotations around this preferred orientation.
Individual evidence
- ↑ David W. James, Richard F. Armishaw: Structure of aqueous solutions: Infrared spectra of the water librational mode in solutions of monovalent halides . In: Australian Journal of Chemistry . 28, No. 6, 1975, p. 1179. doi : 10.1071 / CH9751179 .
- ^ Hideaki Chihara, Takako Shinoda: Librational Motion in Diatomic Molecular Crystals . In: Journal of the Physical Society of Japan . 17, No. 9, 1962, p. 1395. doi : 10.1143 / JPSJ.17.1395 .