The ab initio calculated dipole moment surface and overtone relative intensities of CH chromophore in CHCl3

Relative absorption intensities of the Fermi resonance polyads of isolated CH chromophore for the CHCl3 molecule were calculated with one-dimensional and two-dimensional dipole moment surfaces, which are obtained by the ab in itio density functional method. The calculation showed an unusual strong ab sorption at the second Fermi resonance polyad, which agrees well with the e xperimental data. Such an intensities anomaly can be attributed to the nonl inearity of the dipole moment surface in the vicinity of the equilibrium co nfiguration. By taking advantage of the two-dimensional dipole moment surfa ce where both CH stretching and bending vibrations are taken into considera tion, the nu(1) and 2 nu(4) bands which constitute the first Fermi resonanc e polyad and have little wave function mixture, are found to be of almost e qual intensity. Such a calculation agrees with observations. (C) 2000 Ameri can Institute of Physics. [S0021-9606(00)30614-6].