EFFECTS OF X(3) FRAME VIBRATIONS ON THE CH CHROMOPHORE IN CHX(3) TYPEMOLECULES - HARMONIC COUPLING IN CURVILINEAR INTERNAL COORDINATE APPROACH

Effects of harmonic coupling between X(3) frame vibrations and the CH stretching and bending vibration chromophore in CHX(3) type molecules have been investigated using a curvilinear internal coordinate model. The CH chromophore Hamiltonian used consists of a Morse oscillator Ham iltonian for the CH stretching vibration, two-dimensional isotropic ha rmonic oscillator Hamiltonian for the CH bending vibration, anharmonic bending terms, and Fermi resonance interaction terms between the stre tching and bending vibrations. Van Vleck perturbation theory is used t o take the harmonic coupling terms between the CH chromophore and the X(3) frame vibrations into account. Analytical matrix elements for the perturbation theory contributions have been derived. The model has be en applied to vibrational energy level and infrared absorption intensi ty data for CHD3. Potential energy parameters for the CH chromophore h ave been optimized by a nonlinear least-squares method. The model repr oduces the experimental data well. Only small changes in the potential parameters are observed when the coupling terms due to D atom motions are introduced into the model. The overall conclusion is that it is a good first approximation to ignore the effects of harmonic coupling b etween the CH chromophore and the X(3) frame vibrations in the curvili near internal coordinate model for the CH chromophore in CHX(3) type m olecules.