title: Physisorption of positronium on quartz surfaces.
abstract: Whether positronium (Ps) can be physisorbed on a material surface is of great fundamental interest, since it can lead to new insight regarding quantum sticking and is a necessary first step to try to obtain a Ps2 molecule on a material host. Experiments in the past have produced evidence for physisorbed Ps on a quartz surface, but firm theoretical support for such a conclusion was lacking. We present a first-principles density-functional calculation of the key parameters determining the interaction potential between Ps and an alpha-quartz surface. We show that there is indeed a bound state with an energy of 0.14 eV, a value which agrees very well with the experimental estimate of approximately 0.15 eV. Further, a brief energy analysis invoking the Langmuir-Hinshelwood mechanism for the reaction of physisorbed atoms shows that the formation and desorption of a Ps2 molecule in that picture is consistent with the above results.
authors.affiliation: Department of Physics and Astronomy, Northwestern University, Evanston, Illinois 60208-3112, USA.
authors.forename: R
authors.initials: R
authors.lastname: Saniz
authors.forename: B
authors.initials: B
authors.lastname: Barbiellini
authors.forename: P M
authors.initials: PM
authors.lastname: Platzman
authors.forename: A J
authors.initials: AJ
authors.lastname: Freeman