Knowledge Bank

A theory for describing the rotation-internal rotation spectra of molecules with two equivalent internal rotors of $C2v$ symmetry is developed. Examples are dinitromethane, benzophenone, diphenylsulfone, etc. Starting from a semirigid molecular model the quantum mechanical Hamiltonian and its symmetry group are derived. The lowest eigenvalues are obtained through diagonalization of the truncated irreducible blocks of the energy matrix. Group theoretical arguments are used in the derivation of selection, rules for electric dipole transitions and spin-statistical weights. The characteristics of the microwave and far infrared spectra of such molecules will be shown.