Department of Physics Papers

Document Type

Journal Article

Date of this Version

12-6-2002

Publication Source

Physical Review B

Volume

66

Start Page

214301-1

Last Page

214301-20

DOI

10.1103/PhysRevB.66.214301

Abstract

The calculation of the hindered roton-phonon energy levels of a hydrogen molecule in a confining potential with different symmetries is systematized for the case when the rotational angular momentum J is a good quantum number. One goal of this program is to interpret the energy-resolved neutron time-of-flight spectrum previously obtained for H2C60. This spectrum gives direct information on the energy-level spectrum of H2 molecules confined to the octahedral interstitial sites of solid C60. We treat this problem of coupled translational and orientational degrees of freedom (i) by construction of an effective Hamiltonian to describe the splitting of the manifold of states characterized by a given value of J and having a fixed total number of phonon excitations, (ii) by numerical solutions of the coupled translation-rotation problem on a discrete mesh of points in position space, and (iii) by a group theoretical symmetry analysis. Results obtained from these three different approaches are mutually consistent. The results of our calculations explain several aspects of the experimental observations, but show that a truly satisfactory orientational potential for the interaction of an H2 molecule with a surrounding array of C atoms has not yet been developed.

Comments

At the time of publication, authors Taner Yildirim and A. Brooks Harris were affiliated with the National Institute of Standards and Technology, Gaithersburg, Maryland. Currently, they are faculty members in the Materials Science and Engineering and Physics Departments, respectively, at the University of Pennsylvania.

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Date Posted: 12 August 2015

This document has been peer reviewed.