Direct measurement of the translational mobility of deuterium hydride molecules confined in a model microporous material: AlPO ₄ -5 zeolite

Abstract

We have measured by incoherent quasi-elastic neutron scattering the diffusion coefficient D t of sorbed hydrogen (HD) molecules in the one-dimensional micropore network of AlPO4-5 zeolite. The confined hydrogen phase in such nano-scale cylindrical tubes (diameter φ = 7.3 Å) behaves as a quasi-(1d) fluid phase. At temperature T = 19.5 K, in the medium loading regime (Θ 40%), the translational molecular mobility is quite large, D t = 0.45 • 10 −5 cm 2 s −1 . When increasing Θ, Dt strongly decreases down to 0.03 • 10 −5 cm 2 s −1 (Θ 95%). At lower temperature T = 10.3 K, the HD molecular mobility is still important, Dt = 0.15 • 10 −5 cm 2 s −1 at Θ 40%.

Modeling the processing of interstellar ices by energetic particles

“…In fact, no usable calculation or measurement data could be found on D for D, HD, and D 2 at cryogenic temperatures in an environment similar to interstellar ices. We estimated the coefficients from the available literature on the diffusion of deuterium species in cryogenic temperatures (Guil et al 1973;Kappesser & Wipf 1996;Martin et al 1996;Forsythe & Makri 1998;Kua et al 2001;Coulomb et al 2003). For the sake of convenience D for D and HD, D 2 is expressed as D H or D H 2 , respectively, modified by a multiplier.…”

Diffusion à longue distance

“…Avec H2 , les expériences ont été réalisées entre 70 et 150 K [30,4]. Pour pouvoir faire des mesures au-dessous de 20 K, on peut utiliser la molécule HD [34], étant donné que la séparation entre niveaux de rotation symétriques et antisymétriques n'existe plus.…”