Coupling Among CH Stretching, Bending and Rocking Vibrational Modes in CH2Cl2

Abstract

Infrared absorption spectra of gaseous CH2Cl2 in the regions of 120012000 cm1 were measured using a Bruker IFS 120HR Fourier transform spectrometer in conjunction with a multipass cell. 47 vibrational levels of overtone and combinational spectral lines of the CH stretching (v1, v6), bending (v2), and rocking (v8) modes were analyzed and assigned. Utilizing the normal mode model and considering the coupling among CH stretching, bending and rocking vibrations, values of the harmonic frequency i, the anharmonic constant xij, and the coefficients of Fermi and the Darling-Dennison resonances of v1, v6, v2 and v8 modes were also determined from experimental spectral data with nonlinear least-square fitting. These spectral constants reproduced the experimental levels very well. These results showed that Fermi resonance between CH stretching and rocking vibrations (k188 = 254.63 cm1) is stronger than that between CH stretching and bending vibrations (k122 = 54.87 cm1); and that Darling-Dennison resonances between CH stretching and bending vibrations (k1166 = 215.28 cm1) is also much stronger than that between CH bending and rocking vibrations (k2288 = 5.72 cm1).