HR: 11:50h
AN: V42A-06 INVITED [Abstracts]
TI: Vibrational properties of H-D substituted brucite from experiments and ab initio calculations: a
step towards the prediction of D/H fractionation for complex structures
AU: * Reynard, B
EM: bruno.reynard@ens-lyon.fr
AF: Ecole normale superieure de Lyon, 46 Allee d'Italie, Lyon, 69007, France
AU: Caracas, R
EM: razvan.caracas@ens-lyon.fr
AF: Ecole normale superieure de Lyon, 46 Allee d'Italie, Lyon, 69007, France
AB:
D/H partitioning between water and minerals are often not well constrained from equilibrium experiments, except
for simple hydroxides such as brucite. Vibrational models and experiments can be used to constrain more
accurately isotopic fractionation factors, provided they are first calibrated and tested on relatively simple systems
such as MgO-SiO2-H2O (MSH) starting with brucite Mg(OH)2, then going towards increasing
complexity in minerals like talc Mg3Si4O10(OH)2 and antigorite
Mg48Si34O85(OH)62. We present here first results from combining Raman and IR
spectroscopic and ab initio calculations on brucite. Raman measurements were carried out on significantly
isotopically doped phases, with several intermediate compositions between end-members. Various mode
behaviors are observed, with low frequency modes shifting smoothly in frequency with increasing isotopic
substitution while high frequency modes present a two-mode behavior. The good agreement between predicted
and observed frequencies allows to identify the modes corresponding to those associated to OH-OD vibrations.
Ab initio calculations can thus be used as a guide for deciphering the more complex vibrational spectra such as
those obtained on antigorite; and will help constructing reliable vibrational models of D/H partitioning.
DE: 1011 Thermodynamics (0766, 3611, 8411)
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3934 Optical, infrared, and Raman spectroscopy
DE: 3939 Physical thermodynamics
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting