Overcoming the Rotaional Barrier, Inelastic Neutron Studies of CH4 on MgO
Abstract
We will discuss recent thermodynamic and neutron scattering measurements that probe the rotational motion of methane films on MgO (100) surfaces. We have used the rotational properties of methane at temperatures in the neighborhood of 10K to probe the relative strength of the molecule-molecule and molecule-substrate interactions as a function of layer thickness from one to three layers. We find that near monolayer completion rotational tunneling is evident but no evidence of the bulk- like 0->1 free rotation transition in (excitation near 1.1meV) is found. Once two-layer methane solids begin to form evidence for two distinct features in the excitation spectrum in the region near, but below, 1.0 meV appear. At coverages that exceed three layers, excitations near the bulk free rotor transition appear. We will discuss the implications of this behavior in terms of the relative strength of the interactions and the film properties.
- Publication:
-
APS March Meeting Abstracts
- Pub Date:
- March 2004
- Bibcode:
- 2004APS..MARD35005L