The infrared spectra of the 2ν8, ν2+ ν8, and 2ν2bands of methylene chloride have been recorded both for isotopically pure CH235Cl2and for a natural mixture with a resolution of 0.0044 cm−1in the range 2450–2900 cm−1using a Bruker IFS 120 HR Fourier transform interferometer. The 2ν8overtone band was shown to be unperturbed. Weak global perturbations were observed, however, in the ν2+ ν8combination band, probably due to Fermi or Coriolis interaction with a distant perturber. The 2ν2overtone was found to be locally perturbed, and a crossing aroundK′a= 10 with a perturbing level was evident from a line-by-line analysis. A satisfactory analysis of 2ν2has been obtained by including anx-Coriolis interaction with a vibrational level ofA2symmetry, presumably the ν2+ ν4+ ν5combination 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'sA-reduction Hamiltonian in theIrrepresentation. In addition a hot-band starting from the lowest lying vibrational level, ν4, the 2ν8+ ν4− ν4band, has been partially analyzed. Vibrational shifts of the CH372Cl35Cl isotopic species have been obtained from difference spectra (i.e., spectra of natural abundant CH2Cl2minus those of isotopically pure CH352Cl2). In particular a full rotational analysis of the 2ν8band of the CH372Cl35Cl isotopomer has been performed. Unfortunately, the spectral features due to the CH372Cl2isotopomer were too weak (about 6 times weaker than those of CH372Cl35Cl) to be observed.
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