parahydrogen noun.
[parǝ'hʌɪdrǝdʒ(ǝ)n] E20.[from PARA-1 + HYDROGEN.]Physics. The form of molecular hydrogen in which the two nuclei in the molecule have antiparallel spins (so that the spectrum exhibits no hyperfine structure) and which forms about 25 per cent of hydrogen under normal conditions. Cf.
ORTHOHYDROGEN.
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