SOME PROPERTIES OF EIGENVECTOR MATRIX IN THEORY OF MOLECULAR VIBRATIONS

The mixing of symmetry coordinates in the normal coordinates is investigated through the eigenvector matrix. It is shown that where a stretching and a bending vibration occur in the same species the bending frequency is nearly pure while the stretching often has considerable bending character. When two stretching or two bending modes occur the mixing is high unless the higher frequency mode is due to considerably larger force constant when it again becomes relatively pure. Using these rules the approximation L12 = L13 = L23 = 0 is applied to some bent XYZ molecules (NSF, NSCl, ONF, ONCl, ONBr). From simple explicit equations the force constants and mean amplitudes of vibration are calculated. Comparison with isotopic data and published force fields show the approximation to be valid. © 1969.