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High resolution FTIR spectra and analysis of the ν4 + ν8 combination band and of the 2ν4 + ν8 − ν4 hot band of CH2 35Cl2

The infrared spectrum of isotopically pure CH2 35Cl2 has been recorded at a resolution of 0.0032 cm−1 (FWHM) in the range 1400–1600 cm−1 with a Bruker IFS 120 HR Fourier transform spectrometer in Wuppertal. Here we report the full rotational analysis of the ν4 + ν8 combination band and of the 2ν4 + ν8 − ν4 hot band, which are essentially unperturbed. Excited state constants up to quartic terms have been obtained for both bands and anharmonicity constants involving ν4 and ν8 have been determined. An accurate value for the ν4 band origin has been determined from the ν4 + ν8 combination band and the ν4 + ν8-ν4 hot band, and successively the anharmonicity constants x 48, x 34, x 49 and x 44 were calculated from hot bands observed in this and previous works. For the CH2 35Cl37 Cl isotopic species, band origins for ν4, ν4 + ν8 and 2ν4 + ν8 have been obtained, by assuming the same anharmonicity constants as for CH2 35Cl2.