Swift and efficient nuclear spin conversion of molecular hydrogen confined in Prussian blue analogs

Abstract

The ortho-isomer of molecular hydrogen (o-H2) was converted to the para-isomer (p-H2) within 600 s by using Prussian blue analogs, {MII3[CrIII(CN)6]2} (MCr; M = Mn and Ni), as nuclear-spin conversion catalysts. The swift conversion was confirmed by in-situ Raman micro-spectroscopy under an H2 gas atmosphere (100 kPa) in a low temperature range (2090 K). The o-p ratio observed in MCr deviated from the theoretical value based on the Boltzmann distribution of H2 in a free rotational state to the para-rich proportion, which suggested the promotion of the o-p conversion at higher temperature.