High Resolution IR Study of the Coriolis Coupling between nu3 and nu9 in CH2 35 Cl37 Cl

The infrared spectra of the nu3 and nu9 bands of methylene chloride have been recorded both for isotopically pure CH2 35 Cl2 and for a natural mixture with a resolution of 0.0025-0.004 cm-1 (FWHM) in the range 600-800 cm-1 using a Bruker IFS 120 HR Fourier Transform interferometer. The Coriolis coupling between the two CCl2 stretching fundamentals nu3 and nu9 has been investigated for the CH2 35 Cl37 Cl isotopic species. An effective coupling constant xi39 c = 0.1975(2) cm-1 results from a full rotational analysis of a difference spectrum, obtained by subtracting the CH2 35 Cl2 room temperature spectrum from that of the natural mixture. A least-mean-squares fit of the data to Watson's A-reduction Hamiltonian in the Ir representation yields a set of accurate effective rotational and distortion constants up to quartic terms for the excited states of both fundamental bands. The standard deviation of the fit was 0.893 x 10(-3) cm-1 .