Study of the perpendicular band intensities of the CH chromophore in CHCl3, CHBr3, and CHI3 with three-dimensional dipole moment surface from densityfunctional calculations

The fundamental and overtone absolute intensities of the perpendicular band of the isolated CH chromophore in chloroform (CHCl3), bromoform (CHBr3), a nd iodoform (CHI3) have been calculated. The calculations were carried out by employing a three-dimensional curvilinear internal coordinate Hamiltonia n and a polynomial expanded three-dimensional dipole moment surface (DMS). The DMS was obtained by a hybrid density functional method. Molecular symme try was used to deduce the appropriate DMS expansion formulas. The calculat ed band intensities were compared with available experimental data. Most pr edicted values are accurate to within a factor of 2.