The tunneling frequencies of the isotopic forms of methane in rare-gas solids Original Research Article

The tunneling frequencies of CH4 and CD4 embedded in rare-gas solids are computed using a Hamiltonian of OO symmetry. The distance between the carbon atom of a CH4 molecule and the nearest-neighbor rare-gas atoms is taken as an empirical parameter and determined by matching the computed and observed J = 0 to J = 1 tunneling frequency. Using this distance, the tunneling frequencies of CH3D embedded in argon and krypton, and CH2D2, CHD3, and CD4 embedded in solid argon are computed. A comparison of the observed and computed tunneling frequencies of these isotopic forms of methane provides evidence of the symmetry of the potential function that should be used for symmetric and asymmetric tops in crystalline fields of cubic symmetry.