Adsorption and Occlusion of Gases by the Low-Temperature Forms of Ice

Abstract

Water vapor condensed on a surface at −196°C in the presence of O2, N2, Ar, or CH4, forms a condensate which, on warming, evolves gas in three temperature ranges. The rate of gas evolution first goes through a maximum between −196° and −125°C probably from release of adsorbed gas due to decrease in surface area of the amorphous ice. A second peak in the gas evolution rate appears in the same temperature range as the formation of cubic ice between −120° and −110°C. The remainder of the occluded gas comes out between −70° and −40° (at 15° rise/min) where cubic ice transforms to the hexagonal form. Nitrogen adsorption isotherms indicate surface areas as high as 241 m2/g for amorphous ice prepared at −196°C, and annealing measurements suggest areas as high as 500 m2/g for lower‐temperature preparations. Water—oxygen mixtures subjected to a microwavedischarge, then condensed at −196° and allowed to warm, evolve as much as 97% of the product oxygen between −70° and −40°C.