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Title: Vibrational spectra of dense, hydrous magnesium silicates at high pressure: Importance of the hydrogen bond angle

Abstract

Changes in configuration and hydrogen bonding are inferred from the complex responses of peak parameters (frequency, width, height, and area) to compression for various hydroxyl groups in dense, hydrous magnesium silicates (DHMS). Stretching frequencies ({nu}{sub 1}) depend not only on both O-H...O bond length but also bond angle, which suggests a need to re-examine frequency-structure relationships at 1 atm. For phase B [Mg{sub 12}{sup VI}Si{sup IV}Si{sub 3}O{sub 19}(OH){sub 2}], {nu} of the most intense OH peak determined from IR spectra at nearly hydrostatic pressures (P) decreases to a minimum at 5 GPa, and then rises to a broad maximum near 35 GPa, whereas {nu} of the other intense peak decreased to a broad minimum near 30 GPa. This behavior shows that compression of phase B initially moves O19 toward H2 on O21 and rotates H1 about O20 away from O19 and toward O21 inside the triangle of O atoms, thus increasing the H1-O20-O19 bond angle (from 12 to 21{degree} at 37 GPa). H-H repulsion rotates H2 outside of the triangle by 11{degree} at 37 GPa. Changes in O-O bond length and H-O-O angle calculated from the trends of OH frequency with increasing pressure are consistent with the relatively incompressible layermore » of SiO{sub 4} tetrahedra. Widths, areas, and heights of the hydroxyl peaks also increase with P (whereas areas of the lattice modes are constant), with H1 being much more affected: This response suggests that the H1 bond bends further with compression. Raman spectra of stoichiometric OH{sup {minus}} modes in superhydrous phase B [Mg{sub 10}{sup VI}Si{sup IV}Si{sub 2}O{sub 14}(OH){sub 4}] roughly parallel these trends, consistent with similarly paired hydroxyls with bend bonds. For phase A [Mg{sub 7}{sup IV}Si{sub 2}O{sub 8}(OH){sub 6}], the Raman OH{sup {minus}} bands depend linearly on P, and with constant peak height with slopes similar to those observed for weak stretching modes of trace H in phase B. This behavior is common and is associated with linear hydrogen bonds and unpaired OH{sup {minus}} groups. Combining this data with previous results reveals systematic, linear relationships of d{nu}/dP{vert_bar}{sub i0} with {nu} that suggest high-polyhedral bulk moduli for DHMS.« less

Authors:
 [1];  [2];  [3];  [4]
  1. Washington Univ., St. Louis, MO (United States). Dept. of Earth and Planetary Sciences
  2. Lawrence Livermore National Labs., CA (United States)
  3. Georgia State Univ., Atlanta, GA (United States). Dept. of Geology
  4. Geophysical Lab., Washington, DC (United States)
Publication Date:
Sponsoring Org.:
USDOE, Washington, DC (United States)
OSTI Identifier:
328321
Resource Type:
Journal Article
Journal Name:
American Mineralogist
Additional Journal Information:
Journal Volume: 84; Journal Issue: 3; Other Information: PBD: Mar 1999
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 36 MATERIALS SCIENCE; MAGNESIUM SILICATES; EARTH MANTLE; COMPRESSIBILITY; MORPHOLOGICAL CHANGES; CHEMICAL BONDS; HYDROGEN; BOND ANGLE; PHASE STUDIES

Citation Formats

Hofmeister, A M, Cynn, H, Burnley, P C, and Meade, C. Vibrational spectra of dense, hydrous magnesium silicates at high pressure: Importance of the hydrogen bond angle. United States: N. p., 1999. Web. doi:10.2138/am-1999-0330.
Hofmeister, A M, Cynn, H, Burnley, P C, & Meade, C. Vibrational spectra of dense, hydrous magnesium silicates at high pressure: Importance of the hydrogen bond angle. United States. doi:10.2138/am-1999-0330.
Hofmeister, A M, Cynn, H, Burnley, P C, and Meade, C. Mon . "Vibrational spectra of dense, hydrous magnesium silicates at high pressure: Importance of the hydrogen bond angle". United States. doi:10.2138/am-1999-0330.
@article{osti_328321,
title = {Vibrational spectra of dense, hydrous magnesium silicates at high pressure: Importance of the hydrogen bond angle},
author = {Hofmeister, A M and Cynn, H and Burnley, P C and Meade, C},
abstractNote = {Changes in configuration and hydrogen bonding are inferred from the complex responses of peak parameters (frequency, width, height, and area) to compression for various hydroxyl groups in dense, hydrous magnesium silicates (DHMS). Stretching frequencies ({nu}{sub 1}) depend not only on both O-H...O bond length but also bond angle, which suggests a need to re-examine frequency-structure relationships at 1 atm. For phase B [Mg{sub 12}{sup VI}Si{sup IV}Si{sub 3}O{sub 19}(OH){sub 2}], {nu} of the most intense OH peak determined from IR spectra at nearly hydrostatic pressures (P) decreases to a minimum at 5 GPa, and then rises to a broad maximum near 35 GPa, whereas {nu} of the other intense peak decreased to a broad minimum near 30 GPa. This behavior shows that compression of phase B initially moves O19 toward H2 on O21 and rotates H1 about O20 away from O19 and toward O21 inside the triangle of O atoms, thus increasing the H1-O20-O19 bond angle (from 12 to 21{degree} at 37 GPa). H-H repulsion rotates H2 outside of the triangle by 11{degree} at 37 GPa. Changes in O-O bond length and H-O-O angle calculated from the trends of OH frequency with increasing pressure are consistent with the relatively incompressible layer of SiO{sub 4} tetrahedra. Widths, areas, and heights of the hydroxyl peaks also increase with P (whereas areas of the lattice modes are constant), with H1 being much more affected: This response suggests that the H1 bond bends further with compression. Raman spectra of stoichiometric OH{sup {minus}} modes in superhydrous phase B [Mg{sub 10}{sup VI}Si{sup IV}Si{sub 2}O{sub 14}(OH){sub 4}] roughly parallel these trends, consistent with similarly paired hydroxyls with bend bonds. For phase A [Mg{sub 7}{sup IV}Si{sub 2}O{sub 8}(OH){sub 6}], the Raman OH{sup {minus}} bands depend linearly on P, and with constant peak height with slopes similar to those observed for weak stretching modes of trace H in phase B. This behavior is common and is associated with linear hydrogen bonds and unpaired OH{sup {minus}} groups. Combining this data with previous results reveals systematic, linear relationships of d{nu}/dP{vert_bar}{sub i0} with {nu} that suggest high-polyhedral bulk moduli for DHMS.},
doi = {10.2138/am-1999-0330},
journal = {American Mineralogist},
number = 3,
volume = 84,
place = {United States},
year = {1999},
month = {3}
}