Vibron propagation and localization determined from infrared combination bands of molecular crystals

Abstract
Infrared spectra of CH4II, SiH4II, and GeH4IV show that localized overtones are produced in the crystal by strongly anharmonic transitions, pairs of propagating vibrons by weakly anharmonic transitions. In CH4II, rotons are also detected. A comparison between these results and unpublished overtone spectra of solid p-H2 is proposed.