NEW HIGH PRESSURE COMPOUNDS IN METHANE-HYDROGEN MIXTURES. M. S. Somayazulu, L. W. Finger, R. J. Hemley and H. K. Mao, Geophysical Laboratory and Center for High Pressure Research, Carnegie Institution of Washington, 5251 Broad Branch Road NW, Washington D.C, 20015.
The effect of chemical interactions in mixtures of molecular systems at high pressures has become the focus of attention recently. Studies on binary molecular systems under high pressure have shown the formation of a variety of van der Waals compounds such as He(N2)11[1], Ar(H2)2[2]. A detailed study carried out on the system CH4-H2 using a combination of single crystal x-ray diffraction, Raman scattering and IR spectroscopy has shown the existence of four new compounds (CH4)2H2, CH4(H2)4, CH4(H2)2 and CH4H2 in this system[3]. Of these, (CH4)2H2 and CH4H2 are found to be stable to pressures of the order of 60 GPa. In addition, it was also possible to crystallize pure methane in a quasi-hydrostatic medium of (CH4)2H2. Single crystal diffraction of methane to pressures of the order of 15 GPa were thus possible. The talk will summarize the phase diagram of this binary system, the structural details of the molecular compounds formed and also discuss the recent results on the structural transitions in pure methane.
[1] W. L. Vos, L. W. Finger, R. J. Hemley, J. Z. Hu, H. K. Mao and J. A. Schouten, Nature 358 (1992) 46-48.
[2] P. Loubeyre, R. LeToullec and J.-P. Pinceaux, Phys. Rev. Lett. 72 (1994) 1360.
[3] M. S. Somayazulu, L. W. Finger, R. J. Hemley and H. K. Mao, Science (in press) (1996)