Energy spectrum of one-particle excitations in liquid dielectrics under high pressures and temperatures

The effect of pressure on the conductivity of molecular liquids (hydrogen, oxygen, and nitrogen) and alkali metals (cesium and rubidium) in the region of the experimentally observed dielectric-metal transition is investigated. It is shown that capture of free electrons by atoms or molecules (resulting in the formation of negative ions) is advantageous from the point of view of energy in liquids under moderately high pressures and temperatures. In spite of the fact that the ionization potential increases with density, the energy of an electron transition to the level of the negative ion decreases and, hence, the forbidden gap also decreases. For high densities, the level of negative ions is broadened and transformed into the conduction band. It is assumed that the exponential dependence of conductivity on density and temperature in the transition region is associated with transfer of quasi-free electrons located at the level of atomic negative ions. The spectrum of negative ions of hydrogen, oxygen, and cesium in the strongly compressed state is determined, and the forbidden gap calculated for these substances is found to be in good agreement with the results obtained for hydrogen and oxygen in single shock-wave experiments.