Knowledge Bank

The study by $Steenbeckeliers1$ of the behavior of the second-order centrifugal distortion constants T of nonlinear XYX molecules with respect to isotopic substitution has been extended to include the cases of (a) the unsymmetrically substituted molecule XYX^{\prime} where X and X^{\prime} are distinct isotopes and (b) the general nonlinear triatomic molecule XYZ. These extensions were found to increase considerably the algebraic complexity of the problem. In order to determine the behavior of higher-order triatomic vibration-rotation constants with respect to isotopic substitution, it is necessary to consider the molecular force field beyond the harmonic approximation, A possible procedure for carrying out such determinations will be outlined.