Anharmonic OH vibrations in brucite; small pressure-induced redshift in the range 0-22 GPa

• Published in: The American mineralogist Vol. 94; no. 11-12; pp. 1687 - 1697
• Main Authors: Mitev, Pavlin D, Gajewski, Grzegorz, Hermansson, Kersti
• Format: Journal Article
• Language: English
• Published: Washington Mineralogical Society of America 01.11.2009; Walter de Gruyter GmbH
• Subjects: anharmonic OH frequencies; bonding; Brucite; Chemistry; Correlation analysis; correlation curve; Crystal structure; electric field; Electric fields; electrical field; equations of state; High pressure; hydrogen bonding; hydrous mineral; hydroxyl ion; infrared spectra; Inorganic Chemistry; Kemi; Mineralogy; Minerals; NATURAL SCIENCES; NATURVETENSKAP; nonsilicates; numerical analysis; Oorganisk kemi; oxides; pressure; Quantum physics; Raman spectra; spectra; vibration; vibrational spectra
• ISSN: 0003-004X; 1945-3027; 1945-3027
• DOI: 10.2138/am.2009.3188

The uncoupled anharmonic OH-stretching vibrational frequency for the layered mineral Mg(OH)2 (brucite) has been calculated in the pressure range 0-22 GPa. Quantum-mechanical electronic structure (DFT) calculations were performed, followed by quantum-mechanical vibrational energy calculations. The following findings emerged: (1) The calculated dν(OH)/dP slope is -4 cm-1/GPa, in agreement with the experimental literature value [taken as the average between the Raman and IR-measured slopes for Mg(OH)2]. (2) The calculated ν(OH) vs. R(O...O) correlation is linear and the slope is much smaller than that of traditional H-bond correlation curves in the literature. (3) The main origin of the small dν/dP and dν/dR(O...O) slopes is the small electric field variation as the mineral layers are pressed toward each other. (4) At high pressure, the OH- ions show some tendency to be tilted with respect to the c axis, and a larger tilt angle leads to a larger ν(OH) downshift. (5) The pressure variation of the D quadrupole coupling constant is approximately -1 kHz/GPa.