High Resolution Spectra and Rotational Analysis of the 2ν8, ν2+ ν8, and 2ν2Bands in Methylene Chloride

✍ Scribed by Marcel Snels

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 233 KB
• Volume: 182
• Category: Article
• ISSN: 0022-2852
• DOI: 10.1006/jmsp.1996.7198

✦ Synopsis

The infrared spectra of the 2n 8 , n 2 / n 8 , and 2n 2 bands of methylene chloride have been recorded both for isotopically pure CH 35 2 Cl 2 and for a natural mixture with a resolution of 0.0044 cm 01 in the range 2450-2900 cm 01 using a Bruker IFS 120 HR Fourier transform interferometer. The 2n 8 overtone band was shown to be unperturbed. Weak global perturbations were observed, however, in the n 2 / n 8 combination band, probably due to Fermi or Coriolis interaction with a distant perturber. The 2n 2 overtone was found to be locally perturbed, and a crossing around K a Å 10 with a perturbing level was evident from a line-by-line analysis. A satisfactory analysis of 2n 2 has been obtained by including an x-Coriolis interaction with a vibrational level of A 2 symmetry, presumably the n 2 / n 4 / n 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, n 4 , the 2n 8 / n 4 0 n 4 band, has been partially analyzed. Vibrational shifts of the CH 37 2 Cl 35 Cl isotopic species have been obtained from difference spectra (i.e., spectra of natural abundant CH 2 Cl 2 minus those of isotopically pure CH 35 2 Cl 2 ). In particular a full rotational analysis of the 2n 8 band of the CH 37 2 Cl 35 Cl isotopomer has been performed. Unfortunately, the spectral features due to the CH 37 2 Cl 2 isotopomer were too weak (about 6 times weaker than those of CH 37 2 Cl 35 Cl) to be observed.