Destruction of Diatomic Bonds by Pressure

Abstract

The pressure necessary to destroy the directional character of chemical bonds has been discussed theoretically for hydrogen. This phenomenon has now been experimentally observed in iodine as a first-order phase transition. The delocalization of the electrons causes the diatomic molecular crystal to be converted to a monatomic metal. The experimental results indicate that the transition occurs at 0.7 megabar pressure, 0.53 relative volume, and 1 ev temperature. This does not mean that upon hydrostatic compression iodine would necessarily have the phase transition at those values, since the temperature dependence and the rate of transition of the phase change have to be considered. An empirical rule for the lengthening of diatomic bonds to metallic bonds was used to calculate at what volume iodine should have its transition. The value obtained was 0.53, in agreement with experimental results; an expansion of 15.8% was assumed for the interatomic spacing in iodine. (B.O.G.)