The 3, 5, 6, and 7 THz resonances of α-glycine.

Using an optically thin single crystal sample, mounted in a cryostat permitting cooling to 6 K, and a synchrotron as a bright light source, exceptionally well defined absorption spectra of well-characterised α-glycine have been obtained in the spectral range 2.5-7.5 THz (approximately 80-240 cm-1). Four separate resonances have been observed, respectively at 93, 152, 188, and 223 cm-1 at the lowest temperature. Each reduces in frequency (redshifts) as temperature increases. The origin of this observed behaviour is attributed to a phonon-mediated anharmonicity in the crystal potential. Crown