HR: 0830h
AN: V31D-0967    [PDF]
TI: In Situ High P-T Raman Spectroscopy and Laser Heating: Applications to Volatiles Under Deep Earth Conditions
AU: * Santoro, M
EM: m.santoro@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd., N.W., Washington D.C., DC 20015 United States
AU: * Santoro, M
EM: m.santoro@gl.ciw.edu
AF: LENS, European Laboratory of Non Linear Spectroscopy, and INFM, Via N. Carrara 1, Sesto Fiorentino, FI I-50019 Italy
AU: Lin, J
EM: j.lin@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd., N.W., Washington D.C., DC 20015 United States
AU: Mao, H
EM: mao@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd., N.W., Washington D.C., DC 20015 United States
AU: Hemley, R J
EM: r.hemley@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd., N.W., Washington D.C., DC 20015 United States
AB: The high P-T behavior of volatile species as CO$_2$, H$_2$O, H$_2$, O$_2$, etc. is essential for understanding the nature of deep planetary interiors. These species are also model systems for physics and chemistry. New in situ techniques are reached to detail the vibrational states, chemical reactivity, and formation of new phases in these systems. We present new measurements of Raman spectra of materials at very high pressure and temperature, in diamond anvil cells, using the laser heating technique. A Nd:YLF laser is employed to heat the samples with a typical power of tens of watts and spot sizes of about 30-40 \micron. For transparent materials, a thin metal Re or Pt foil (10-20 \micron) is employed to absorb efficiently the laser energy and transfer it to the sample. A small hole (10-20 \micron) is drilled through the foil and the sample is uniformly heated, and is investigated by Raman spectroscopy. The temperature of the foil is monitored by mean of a dedicated monochromator-CCD set up, which detects the gray body radiation coming from it. An argon laser is employed as Raman excitation source; a 0.45 focus monochromator and a CCD camera are used to disperse and detect the scattered light respectively. One of the most important goals achieved by this technique was the capability to detect the real sample temperature given by the stokes/antistokes ratio, which typically results lower than that obtained from the grey body radiation. This result opens the way to perform quantitative experiments dealing with the usual high pressure laser heating procedures, and to investigate the thermodynamic properties of the systems with good accuracy. We present preliminary results on solid CO$_2$, as a basic test of our technique. Both the external and internal vibrational frequency regions of the molecular crystal were detected, above 10 GPa and metal foil temperatures as high as 2000 K. The stoks/antistoks balance was achieved from both kinds of excitation. Some important features of the high P-T phase diagram have been clarified. The technique can now be used to study broad range of related materials, including hot dense fluids, at deep mantle conditions.
DE: 3924 High-pressure behavior
DE: 3934 Optical, infrared, and Raman spectroscopy
DE: 3939 Physical thermodynamics
DE: 8147 Planetary interiors (5430, 5724)
DE: 9805 Instruments useful in three or more fields
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting