HIGH-PRESSURE COMPOUNDS IN THE METHANE-HYDROGEN SYSTEM - X-RAY, INFRARED AND RAMAN STUDIES ON CH4(H-2)(2)

Recent high pressure experiments on the binary system CH4-H-2 have rev ealed a rich phase diagram including the existence of at least four st oichiometric solid phrases to 60 GPa (and 300 K). Raman, x-ray, and in frared measurements as a function of both pressure and composition all ow us to examine the origin of the stability of these van der Waals co mpounds and the nature of the relevant intermolecular interactions. In this paper, we present results on one of the four compounds of methan e and hydrogen. Experimental evidence for changes in stoichiometry of the compound CH4(H-2)(4) with increasing pressure is presented. Ramon spectra of one of the compounds has shown the existence of site depend ent vibrational coupling of the hydrogen molecules. In particular, our infrared measurements show that charge transfer effects occur in thes e molecular compounds at higher pressures suggesting changes in the ch aracter of intermolecular interactions with increasing pressure.