DENSITY-FUNCTIONAL COMPUTATIONS OF THE DIPOLE-MOMENT DERIVATIVES FOR HALOGENATED METHANES

Electric dipole moments for the equilibrium molecular structures and their derivatives along the symmetry coordinates of vibration were computed for CH2F2, CD2F2, CH2Cl2, CD2Cl2, CF2Cl2, CH3F, CD3F, CH3Cl, CD3Cl, CHF3, CDF3, CHCl3, CDCl3, CFCl3, CF3Cl, CF4, and CCl4 by means of the deMon density functional program (St-Amant, A.; Salahub, D. R. Chem. Phys. Lett. 1990, 169, 387). A satisfactory agreement was found between the experimental and computed dipole moments for the equilibrium molecular structures. Perfect agreement was found between the rotational corrections to the dipole moment derivatives calculated by deMon and those obtained independently from the permanent dipole moment and the orthogonality relations between the symmetry coordinates and the rotational coordinates. Using force constants which are available from the literature, derivatives of the dipole moments were transformed into the representation of the normal coordinates of vibration, and the results were compared with the experimental data on the infrared intensities. Density functional computations provide reliable information on the relations between the signs of the dipole moment derivatives and in most cases also on their absolute values in the series of investigated molecules.