High-pressure IR spectra of lattice modes and OH vibrations in Fe- bearing wadsleyite

High-pressure infrared (IR) spectra of most lattice modes and of hydrous impurities of Fe-bearing wadsleyite were measured from 0 to 23 GPa. The pressure dependence of eight OH vibrations were established to 12 GPa. The degree of hydrogen bonding is inferred from the values of the hydroxyl frequencies and their response to pressure: Five hydroxyls with low ν have negative ∂ν/∂P and thus moderate to strong hydrogen bonding, whereas three OH groups with high ν have near-zero or positive values of ∂ν/∂P and thus weak or no hydrogen bonding. This information, the response of the OH bands to Fe/Mg exchange, and X-ray data were used to assign the most intense OH bands to the structural sites, O(1) and O(2). -from Authors