AUTHOR=Ueta Hirokazu , Fukutani Katsuyuki , Yamakawa Koichiro 

TITLE=Fast ortho-to-para conversion of molecular hydrogen in chemisorption and matrix-isolation systems

JOURNAL=Frontiers in Chemistry

VOLUME=11

YEAR=2023

URL=https://www.frontiersin.org/journals/chemistry/articles/10.3389/fchem.2023.1258035

DOI=10.3389/fchem.2023.1258035

ISSN=2296-2646

ABSTRACT=<p>Molecular hydrogen has two nuclear-spin modifications called <italic>ortho</italic> and <italic>para</italic>. Because of the symmetry restriction with respect to permutation of the two protons, the <italic>ortho</italic> and <italic>para</italic> isomers take only odd and even values of the rotational quantum number, respectively. The <italic>ortho</italic>-to-<italic>para</italic> conversion is promoted in condensed systems, to which the excess rotational energy and spin angular momentum are transferred. We review recent studies on fast <italic>ortho</italic>-to-<italic>para</italic> conversion of hydrogen in molecular chemisorption and matrix isolation systems, discussing the conversion mechanism as well as rotational-relaxation pathways.</p>