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

Electric dipole moments for the equilibrium molecular structures and t heir derivatives along the symmetry coordinates of vibration were comp uted for CH2F2, CD2F2, CH2Cl2, CD2Cl2, CF2Cl2, CH3F, CD3F, CH3Cl, CD3C l, CHF3, CDF3, CHCl3, CDCl3, CFCl3, CF3Cl, CF4, and CCl4 by means of t he deMon density functional program (St-Amant, A.; Salahub, D. R. Chem . Phys. Lett. 1990, 169, 387). A satisfactory agreement was found betw een the experimental and computed dipole moments for the equilibrium m olecular structures. Perfect agreement was found between the rotationa l 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 rota tional coordinates. Using force constants which are available from the literature, derivatives of the dipole moments were transformed into t he representation of the normal coordinates of vibration, and the resu lts were compared with the experimental data on the infrared intensiti es. Density functional computations provide reliable information on th e relations between the signs of the dipole moment derivatives and in most cases also on their absolute values in the series of investigated molecules.