北京高压科学研究中心
Center for High Pressure Science &Technology Advanced Research

4.6 ZHENG Haiyan

Chemical reactions of the carbon in volatile molecules under extreme pressure


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Besides elemental carbons including the graphite, diamond, nanotube and fullerene, organic molecules are also very important forms of carbon. Under geophysical conditions, the organics may undergo chemical reactions that result in significant effect on the carbon cycle in deep earth, or in the interiors of larger planets in solar system. Here, we will present the chemical reaction process of typical unsaturated compounds in the C-H and C-H-N systems, including aromatic molecules, acetylene and acetonitrile to highlight the basic reaction rule under high pressure. By exploring the in situ spectroscopy, diffraction technology combined with chemical analysis such as  solid state NMR, pair distribution function and gas-chromatography mass-spectrometry, we found the common features of the reactions include: 1, the polymerizations typically happened at around 20 GPa, which is corresponding to the pressure of the transition zone or the uppermost part of the lower mantle; 2, the reactions are directed by the crystal structures of the reactant; 3, the unsaturated compounds will transfer into the saturated framework by addition reaction, from C(sp) to C(sp2) and C(sp3); 4, the hydrogen atoms may bond to each other or nitrogen atom, and small molecules are then eliminated, which will produce the unsaturated species again.