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Science 1 October 1999:
Vol. 286. no. 5437, pp. 100 - 102
DOI: 10.1126/science.286.5437.100
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Reports

Dissociation of CH4 at High Pressures and Temperatures: Diamond Formation in Giant Planet Interiors?

Laura Robin Benedetti, 1 Jeffrey H. Nguyen, 4 Wendell A. Caldwell, 2 Hongjian Liu, 2 Michael Kruger, 5 Raymond Jeanloz 23

Experiments using laser-heated diamond anvil cells show that methane (CH4) breaks down to form diamond at pressures between 10 and 50 gigapascals and temperatures of about 2000 to 3000 kelvin. Infrared absorption and Raman spectroscopy, along with x-ray diffraction, indicate the presence of polymeric hydrocarbons in addition to the diamond, which is in agreement with theoretical predictions. Dissociation of CH4 at high pressures and temperatures can influence the energy budgets of planets containing substantial amounts of CH4, water, and ammonia, such as Uranus and Neptune.

1 Department of Physics,
2 Department of Geology and Geophysics,
3 Department of Astronomy and Miller Institute for Basic Research in Science, University of California, Berkeley, CA 94720, USA.
4 H-Division, Physics Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94551, USA.
5 Department of Physics, 4747 Troost, Room 227, University of Missouri, Kansas City, MO 64110, USA.

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