A molecule is like a three-dimensional rigid body with its constituent atoms glued together by chemical bonds. The classical dynamic nature of a molecule is characterized by the translational motion of its center of mass and rotation around the center of mass, parameterized by the three Euler angles { }φ θ ψ, , (Goldstein (1964). The rotation involves a symmetry axis or a set of symmetry axes. The symmetry axis of a linear molecule, e.g., CO, is the line joining the two atoms, in this case carbon and oxygen. For a spherical molecule, any direction in space can act as a symmetry axis.