Fermi resonances in overtone spectra of bromoform, CHBr3

A curvilinear internal coordinate Hamiltonian is used to analyze Fermi resonances between CH stretching and bending vibrations in bromoform. Besides the usual Fermi resonance terms, cubic and quartic kinetic and potential energy terms in bending variables are included in the Hamiltonian. The eigenvalues are obtained variationally with a Morse oscillator basis set for the stretch and a two-dimensional harmonic oscillator basis set for the bend. The potential energy parameters are optimized with the nonlinear least squares method. A bond dipole model is used to calculate infrared absorption intensities. The model reproduces well the observed vibrational term values and infrared absorption intensities.