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Diffusion of hydrogen fluoride in solid parahydrogen

“…The typical value of H v /k B in solid pH 2 is estimated both experimentally and theoretically to be approximately 100 K. 6,8,22,23 The factor g I exp(S v /k B ) is 1 in the order of magnitude. 18,22 Equation (4) indicates that the rate of diffusion via thermally equilibrated vacancies must show the Arrhenius-type temperature dependence with the activation energy of ∼100 K even if exchange between HF and vacancies is quantum process.…”

“…7 They also concluded that the temperature dependence between 7 and 10 K can be interpreted as migration by particle-vacancy exchange in which the vacancy is formed thermally, but moves by tunneling. Miyazaki and co-workers [8][9][10] have studied the diffusion of hydrogen atoms in solid pH 2 around 4 K by ESR measurement and found that hydrogen atoms can migrate by tunneling exchange of chemical bonds H + H 2 → H 2 + H. It should be noted that quantum diffusion or rotation diffusion of orthohydrogen (oH 2 ) in solid pH 2 discussed by Van Kranendonk 1 is a different phenomenon from what we are discussing, because rotation diffusion is not diffusion of real particles but the conversion of ortho-para into para-ortho pairs due to the magnetic dipole-dipole interaction between the nuclear spins in neighboring molecules.…”

Molecular Photodynamics in Rare Gas Solids

“…(e) Tunneling mobility is mainly reserved to quantum hosts, such as solid H 2 and He, in which it has been shown that this is the main mechanism for the migration of vacancies . Vacancies in turn serve as the means for both self-diffusion and interdiffusion of impurities such as H atoms in solid H 2 . , Tunneling via both physical exchange , and chemical exchange has been considered for H-atom diffusion theoretically and has been used to rationalize the extensive measurements by the Miyazaki group in pure and isotopically mixed solids of hydrogen. − Tunneling contributions to H-atom diffusion in heavier rare gases, although not significant, have been suggested as a possibility. , …”

“…24,25 Tunneling via both physical exchange 26,27 and chemical exchange 28 has been considered for H-atom diffusion theoretically and has been used to rationalize the extensive measurements by the Miyazaki group in pure and isotopically mixed solids of hydrogen. [29][30][31][32] Tunneling contributions to H-atom diffusion in heavier rare gases, although not significant, have been suggested as a possibility. 33,34 The nature of the barrier crossed in these cases varies dramatically.…”