The science is in the squeezing; under normal atmospheric conditions, the molecules of xenon difluoride keep a respectable distance from one another. But under the intense pressures produced by the diamond anvils the molecules are forced together into metallic 3-D structures. At one million atmospheres -- roughly equivalent to the pressure found halfway to the center of the Earth -- the xenon difluoride is pressed neatly into these structures where the mechanical energy of all that pressure is stored in the chemical bonds between the molecules.