title: Diffusion of hydrogen fluoride in solid parahydrogen.
abstract: We studied diffusion of hydrogen fluoride (HF) in solid parahydrogen (pH2) around 4 K. Diffusion rates were determined from time dependence of FT-IR spectra of HF monomers. The absorption of HF monomers shows temporal decay due to dimerization reaction via diffusion. It was found that the rates are affected by the sample temperature, the initial HF concentration, and annealing of samples. The observed non-Arrhenius-type temperature dependence suggests that the diffusion is dominated by a quantum tunneling process, that is, "quantum diffusion." Deceleration of the diffusion in condensed samples and acceleration in annealed samples were also observed. These results can be attributed to the fact that lower periodicity of samples due to impurities or defects suppresses the quantum tunneling. It seems to be difficult to explain the observed dependences by three possible diffusion mechanisms, exchange of chemical bonds, direct cyclic exchange, and exchange with mobile vacancy. Therefore, we propose a hypothetical mechanism by exchange of vacancies originating from quantum effect.
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama 700-8530, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Ooe
authors.forename: Yuki
authors.initials: Y
authors.lastname: Miyamoto
authors.forename: Susumu
authors.initials: S
authors.lastname: Kuma
authors.forename: Kentarou
authors.initials: K
authors.lastname: Kawaguchi
authors.forename: Kyo
authors.initials: K
authors.lastname: Nakajima
authors.forename: Itsuo
authors.initials: I
authors.lastname: Nakano
authors.forename: Noboru
authors.initials: N
authors.lastname: Sasao
authors.forename: Jian
authors.initials: J
authors.lastname: Tang
authors.forename: Takashi
authors.initials: T
authors.lastname: Taniguchi
authors.forename: Motohiko
authors.initials: M
authors.lastname: Yoshimura
mesh_terms: D004058:Diffusion; D006858:Hydrofluoric Acid / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry*; D013696:Temperature
chemical_list: D006859:Hydrogen; D006858:Hydrofluoric Acid