Liquid Carbon Chemistry

The chemistry of carbon atoms, with their gregarious ability to bond to four other atoms, is a major determinant of life on Earth. But what happens when carbon is heated up to its melting temperature of 5000 K at pressures greater than 100 bars? Although liquid carbon may exist inside the planets Neptune and Uranus, the main interest in studying liquid carbon here on Earth might be in the indirect information provided about bonding in ordinary solid carbon or in hypothetical novel forms of solid carbon A new experiment creates liquid carbon by blasting a solid sheet of C with an intense laser beam. Before the liquid can vaporize, its structure is quickly probed by an x-ray beam. At low carbon density, two bonds seem to be the preferential way of hooking up, while at higher density, three and four bonds are typical.

This is not to say that complex organic molecules (carbon bonded to other atoms such as hydrogen or oxygen) could survive at 5000 K, but carbon bonds are tougher and can persist. The experiment was performed by physicists from UC Berkeley, the Paul Scherrer Institute (PSI) in Switzerland, Lawrence Berkeley National Lab, Kansas State, and Lawrence Livermore National Lab. A team member, Steve Johnson (steve.johnson@mailaps.org), says that one next step will be to study carbon, as well as other materials, at even higher temperatures in order to look at "warm dense matter," a realm of matter too hot to be considered by conventional solid-state theory but too dense to be considered by conventional plasma theory. (Johnson et al., Physical Review Letters,11 February 2005; lab website at http://www.physics.berkeley.edu/research/falcone/ )