Spectra containing P and R branches can be analyzed by allowing for (*) vibrations to be coupled to the motion described by this system; those branches correspond to the delta J equals plus or minus one selection rule for this system.
n a less constrained version of this system, the distortion constant D equals four times B cubed over omega squared. Energy levels in this system are split by 2 times B, where B equals Planck's constant over the quantity eight pi squared c times I. Molecules are classified as spherical, symmetric, or asymmetric variants of this system in microwave spectroscopy, as this system generally absorbs light in the microwave region. Spectra containing P and R branches can be analyzed by allowing for (*) vibrations to be coupled to the motion described by this system; those branches correspond to the delta J equals plus or minus one selection rule for this system. The wavefunction for this system equals a normalized complex exponential times an associated Legendre polynomial. For10 points, name this quantum mechanical model with a wavefunction fully described by spherical harmonics, which treats a diatomic molecule as having a fixed bond length and only rotational motion.
n a less constrained version of this system, the distortion constant D equals four times B cubed over omega squared.
rigid rotor [or  rigid rotator]