Ortho and Parahydrogen in Interstellar Material

Abstract

Abstract Since H2 is the most abundant molecule in the universe, the ratio of orthohydrogen molecules to parahydrogen in interstellar space is of interest. H2, formed by any exothermic reaction will be in the ratio of 3: 1 according to their statistical weight. This corresponds to the high temperature equilibrium. At the low prevailing temperatures of interstellar space, the thermo-dynamic equilibrium should be shifted to the parahydrogen side. In the gas phase this shift can occur only over chemical reactions which are close to thermally neutral. In addition, it can be concluded that two ion scrambling reactions dominate the process and these both involve positive hydrogen ions. In special cases, surface catalysis on interstellar dust particles may add to the equilibrating process. The highly forbidden process of transition by radiation J = 1(ortho) → J = O(para) + hv can only play a minor role in this catalysis