Vibrations of the OH Ions in Muscovite

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Abstract
Pleochroism of the infrared absorption of muscovite has been measured under moderate resolution. The results are discussed in terms of the idealized mica structure. From the pleochroism of the OH stretching band, orientation of the vibrational transition moments can be determined. These moments are tilted out of the cleavage plane by about 16°. Their projection onto the cleavage plane makes an angle of about 32° with the b axis. These directions furnish approximations to the orientation of the OH ions, but the danger of equating the two is stressed. Vibrational coupling is small. This result has been used to decide rather conclusively between two models of muscovite which differ in the orientation of the OH ions. The librational motion has been studied directly, as well as in combination bands with the OH fundamental. It is shown that the SiO lattice also gives rise to combination bands with νOH.

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