The vibration of the methane molecule is composed of 9 normal modes. Four modes are stretching the molecule along all four covalently bound C and H atoms. The other five modes describe some kind of angular deformation. Three of the four stretching modes are antisymmetric with respect to a S₄ improper axis. These modes are triply degenerate (they have the same vibrational frequency), which makes them indistinguishable in usual experiments. Thus, we only speak of one antisymmetric stretching ν₃(F₂). The remaining, symmetric stretching ν₁(A₁) is non-degenerate and symmetric with respect to the all S₄ improper axes. Two of the five deformation modes are symmetric with respect to a C₂ axis. These modes are doubly degenerate and we speak of one symmetric deformation ν₂(E). The remaining, antisymmetric deformation modes are antisymmetric with respect to the C₂ axes, and triply degenerate, which is why we speak of only one antisymmetric deformation ν₄(F₂).

Methane is in the T_d point group with the symmetry elements: three S₄ improper axes (blue), four C₃ axes (red), three C₂ axes (black), six σ_v planes (cyan). [check symotter-gallery]