High resolution spectra and rotational analysis of the 2 nu(8), nu(2)+nu(8) and 2 nu(2) bands in methylene chloride

The infrared spectra of the 2 nu(8), nu(2) + nu(8), and 2 nu(2) bands of methylene chloride have been recorded both for isotopically pure (CH2Cl2)-Cl-35 and for a natural mixture with a resolution of 0.0044 cm(-1) in the range 2450-2900 cm(-1) using a Bruker IFS 120 HR Fourier transform interferometer. The 2 nu(8) overtone band was shown to be unperturbed. Weak global perturbations were observed, however, in the nu(2) + nu(8) combination band, probably due to Fermi or Coriolis interaction with a distant perturber. The 2 nu(2) overtone was found to be locally perturbed, and a crossing around K-a' = 10 with a perturbing level was evident from a line-by-line analysis. A satisfactory analysis of 2 nu(2) has been obtained by including an x-Coriolis interaction with a vibrational level of A(2) symmetry, presumably the nu(2) + nu(4) + nu(5) combination band. A full rotational analysis for all bands has been carried out, yielding accurate effective rotational and distortion constants up to quartic terms for the excited states using Watson's A-reduction Hamiltonian in the I-r representation. In addition a hot-band starting from the lowest lying vibrational level, nu(4), the 2 nu(8) + nu(4) - nu(4) band, has been partially analyzed. Vibrational shifts of the (CH2ClCl)-Cl-37-Cl-35 isotopic species have been obtained from difference spectra (i.e., spectra of natural abundant CH2Cl2 minus those of isotopically pure (CH2Cl2)-Cl-35). In particular a full rotational analysis of the 2 nu(8) band of the (CH2ClCl)-Cl-37-Cl-35 isotopomer has been performed. Unfortunately, the spectral features due to the (CH2Cl2)-Cl-37 isotopomer were too weak (about 6 times weaker than those of (CH2ClCl)-Cl-37-Cl-35) to be observed.