| 释义 |
orthohydrogen
(stress variable)
Also ortho hydrogen and with hyphen.
[f. ortho- + hydrogen as tr. G. orthowasserstoff (Bonhoeffer & Harteck 1929, in Naturwissenschaften XVII. 182/1), coined on the analogy of orthohelium (see quot. 1935).]
The form of molecular hydrogen in which the two nuclei in the molecule have parallel spins, so that the spectrum exhibits a hyperfine structure of triplets; it differs slightly in physical properties from the other form (parahydrogen) and forms 75 per cent of hydrogen in equilibrium at room temperature.
1929Chem. Abstr. XXIII. 2614 (heading) Experiments on para- and ortho-hydrogen. 1935A. Farkas Orthohydrogen, Parahydrogen & Heavy Hydrogen ii. 4 The parahydrogen molecules have antiparallel nuclear spins and even rotational quantum numbers, while the orthohydrogen molecules possess parallel nuclear spins and odd rotational quantum numbers. Ibid., 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. 1962P. J. & B. Durrant Introd. Adv. Inorg. Chem. xiii. 368 Ordinary hydrogen gas is a tautomeric mixture of orthohydrogen and parahydrogen. 1966D. H. Whiffen Spectroscopy ix. 114 In the absence of magnetic materials non-equilibrium mixtures of ortho and para hydrogen are stable for many months. 1969H. T. Evans tr. Hägg's Gen. & Inorg. Chem. xviii. 452 At 0°K..only parahydrogen exists at equilibrium. |