Rotational excitations of methane molecules in a nonequilibrium krypton matrix

The rotational transitions of 1.5% CH4 isolated in a Kr matrix by condensing the mixed gas onto a cold (T=7 K) surface have been measured in the energy range <1.2 meV using a high resolution neutron scattering technique. The spectra are similar to those observed with CH4/ Ar. Most methane molecules are found at weakly disturbed substitutional fcc and hcp sites with weak rotational potentials. About 30% of the molecules are on disordered sites and display a broad distribution of stronger potentials.