Fizika Nizkikh Temperatur: Volume 43, Number 12 (December 2017), p. 1687-1706    ( to contents , go back )

Isotopic and spin-nuclear effects in solid hydrogens

Yuri A. Freiman

B. Verkin Institute for Low Temperature Physics and Engineering of the National Academy of Sciences of Ukraine 47 Nauky Ave., Kharkiv 61103, Ukraine
E-mail: yuri.afreiman@gmail.com

Yanier Crespo

International Center for Theoretical Physics (ICTP), IT-34014 Trieste, Italy
E-mail: yanier@hotmail.com

Received April 2, 2017

Abstract

The multiple isotopic family of hydrogens (H2, HD, D2, HT, DT, T2) due to large differences in the de Boer quantum parameter and inertia moments displays a diversity of pronounced quantum isotopic solid-state effects. The homonuclear members of this family (H2, D2, T2) due to the permutation symmetry are subjects of the constraints of quantum mechanics which link the possible rotational states of these molecules to their total nuclear spin giving rise to the existence of two spin-nuclear modifications, ortho- and parahydrogens, possessing substantially different properties. Consequently, hydrogen solids present an unique opportunity for studying both isotope and spin-nuclear effects. The rotational spectra of heteronuclear hydrogens (HD, HT, DT) are free from limitations imposed by the permutation symmetry. As a result, the ground state of these species in solid state is virtually degenerate. The most dramatic consequence of this fact is an effect similar to the Pomeranchuk effect in 3He which in the case of the solid heteronuclear hydrogens manifests itself as the reentrant broken symmetryphase transitions. In this review article we discuss thermodynamic and kinetic effects pertaining to different isotopic and spin-nuclear species, as well as problems that still remain to be solved.

PACS: 67.80.ff Molecular hydrogen and isotopes.

Key words: isotopic family of hydrogens, homo- and heteronuclear species, ortho- and parahydrogens, isotope and spin-nuclear effects, ortho- and para conversion, Pomeranchuk effect, reentrant broken symmetry phase transition.

Published online: October 25, 2017

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