parahydrogenn.
/ˌparəˈhʌɪdrədʒ(ə)n/, U.S. /ˌpɛrəˈhaɪdrədʒ(ə)n/ Chemistry.
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 n.
ΘΚΠ
the world > matter > chemistry > elements and compounds > hydrogen > [noun] > molecular
orthohydrogen1929
parahydrogen1929
1929 Chem. Abstr. 23 2614 (heading) Experiments on para- and ortho-hydrogen.
1935 A. Farkas Orthohydrogen, Parahydrogen & Heavy Hydrogen ii. 4 The names orthohydrogen and parahydrogen were chosen by Bonhoeffer and Harteck on analogy with the nomenclature for the helium atom (orthohelium and parahelium), but it must be emphasized that the distinction between the hydrogen modifications is based on the different orientations of the nuclear spins, while in the case of helium it depends on the orientation of the electron spins.
1969 H. T. Evans tr. G. Hägg Gen. & Inorg. Chem. xviii. 452 The melting and boiling points of parahydrogen are approximately 0·1° lower than for ordinary hydrogen.
1996 Jrnl. Physical Chem. 100 12135/1 Solid parahydrogen has recently been shown to be a promising medium for matrix-isolation spectroscopy.
This entry has been updated (OED Third Edition, June 2005; most recently modified version published online March 2022).
<
n.1929