On the relation between the operators of physical quantities of a nonrigid molecule and the symmetry of its equilibrium configurations

The problem of changes in the expressions for effective operators of physical quantities (including an effective Hamiltonian) of a nonrigid molecule upon a change in its equilibrium configurations, in the case in which different possible geometries of such configurations correspond to different point groups, is considered for the example of the nonrigid dimethylacetylene molecule CH3C2CH3 in the ground electronic state.