FLEXIBLE MODELS FOR INTRA-MOLECULAR MOTION, A VERSATILE TREATMENT AND ITS APPLICATION TO GLYOXAL

As a tool for the interpretation of molecular spectroscopic data, a direct numerical treatment is presented for arbitrary one- and two-dimensional internal motions of an arbitrary non-linear molecule. Wavefunctions and energy levels consistent with the underlying model are calculated for J = 0 and J = 1 for comparison with observed intramolecular motion spectra and shifts of rotational constants associated with excitation of such motions. Numerical methods include a mesh point representation based on trigonometric interpolation and a matrix iteration technique for large eigenvectors (N ∼ 1000) yielding eigenvalues accurate to at least 10 decimal digits. An application to trans-glyoxal explains, for the first time, the shifts of all three rotational constants upon torsional (ν7) excitation by Coriolis interaction with the ν12 mode and a shrinking of CCO angles upon torsion. The main use of the method will be the derivation of spectroscopic data from theoretical predictions on potential surfaces and minimum energy pathways or surfaces of motion for comparison with experiment. © 1979.