title: Helium diffusion through H2O and D2O amorphous ice: observation of a lattice inverse isotope effect.
abstract: The diffusion of He through both H2O and D2O amorphous solid water (ASW) has been measured between 55 and 110 K. We find the diffusion rate is dependent on the isotopic composition of the ASW lattice. This lattice isotope effect is the "inverse" of a normal isotope effect in that diffusion is faster in the heavier (D2O) isotope. Transition state theory calculations show that the inverse isotope effect is due to a tight transition state and predominantly arises from the zero-point vibrational energy associated with the frustrated rotational modes of water in the lattice.
authors.affiliation: Pacific Northwest National Laboratory, Fundamental Sciences Directorate, P.O. Box 999, Mail Stop K8-88, Richland, Washington 99352, USA.
authors.forename: John L
authors.initials: JL
authors.lastname: Daschbach
authors.forename: Gregory K
authors.initials: GK
authors.lastname: Schenter
authors.forename: Patrick
authors.initials: P
authors.lastname: Ayotte
authors.forename: R Scott
authors.initials: RS
authors.lastname: Smith
authors.forename: Bruce D
authors.initials: BD
authors.lastname: Kay