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Orthohydrogen
*** Shopping-Tip: Orthohydrogen
Orthohydrogen and Parahydrogen
A
hydrogen molecule (H
2) is made up of two
atoms of hydrogen linked by a
covalent bond. If we neglect the traces of
deuterium and
tritium which could be present, each hydrogen atom is constituted of a single
proton and a single
electron (this is called '''light hydrogen'''; the term
protonium designates an exotic atomic state consisting of a
proton and an
antiproton). The proton has an associated
magnetic moment, which we can treat as being generated by the proton's spin. The H
2 molecule can thus have its protons aligned in either the same direction (this is '''orthohydrogen''') or in opposite directions (this is '''parahydrogen''').
Orthohydrogen is unstable at low temperatures, and spontaneously changes into parahydrogen with time, a process which releases
heat; an undesirable occurrence when one wants hydrogen to remain liquid. At standard (room) temperature, hydrogen is made up of 75% orthohydrogen, a proportion which the liquefaction process preserves. One must therefore use a
catalyst to accelerate the conversion of the liquid hydrogen into parahydrogen, or supply additional refrigeration equipment to absorb the heat that the liquid hydrogen will give off as it spontaneously converts itself to pure parahydrogen.
fr:Orthohydrogène
