Anharmonic cubic force field of methane

Anharmonic Klambda mu nu parameters of the CH4 molecule potential function are derived from the experimental rotational, tetrahedral splitting and resonance parameters of CH4 and CH2D2. As an illustration of the correctness of the potential parameters obtained, the original spectroscopic constants of CH4 and CH2D2 are theoretically reproduced. Calculations of the spectroscopic constants of CH3D and CHD3 molecules are also given for illustrations.