Influence of Vibrations on Molecular Structure Determinations. III. Inertial Defects

Abstract

The relationships between various types of moments of inertia and vibration—rotation corrections are developed from general theory, with emphasis on the qualitative physical features and the quantities which may be calculated without knowledge of anharmonic force constants. The inertial defects of planar triatomic and tetratomic molecules and nonplanar molecules with a plane of symmetry are considered, and it is found that simple approximations, which depend mainly on the one or two modes of lowest frequency, give results within 10%—20% of the experimental values. The application of inertial defect corrections in structure analysis is illustrated for the calculation of HH distances in CH2Cl2, SiH2F2, and CH3CXO molecules (X = H, F, Cl, Br).