Controlling and measuring the concentration of para-D2 is an essential steptoward realizing solid deuterium as an intense ultra-cold neutron (UCN) source.To this end, we implemented an experimental technique to convert para- toortho-deuterium molecules by flowing D2 gas through a cryogenic cell filledwith paramagnetic hydrous ferric oxide granules. This process efficientlyreduced the para-D2 concentration from 33.3% to 1.5%. Rotational Ramanspectroscopy was applied to measure the residual para-D2 contamination tobetter than 2 parts in 10^3, and the hydrogen contamination to 1 part in 10^3.We also contrast our optical technique to conventional thermal conductivitymeasurements of the para-D2 concentration, reporting some of the relevantstrengths and weaknesses of our implementation of each technique.
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