The structure and thermal properties of novel mesoporous inert-gas solids were studied by synchrotron x-ray diffraction. The materials were prepared by injecting a jet of helium containing dilute amounts of inert atoms and molecules (Ne, Kr, N2) into superfluid helium. The characteristic size of the constituent building blocks is 60 , and the density is >1020 impurity atoms per cm3. The Kr and N2 solids are stable outside of liquid He, up to temperatures above 10 K. These materials may find various applications as a new type of porous medium for fundamental physics, as well as in cluster physics, matrix isolation spectroscopy, and catalysis of low temperature chemical reactions. 1997 The American Physical Society.
