High resolution IR study of the coriolis coupling between nu(3) and nu(9) in (CH2ClCl)-Cl-35-Cl-37

The infrared spectra of the nu(3) and nu(9) bands of methylene chloride have been recorded both for isotopically pure (CH2Cl2)-Cl-35 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 nu(3) and nu(9) has been investigated for the (CH2ClCl)-Cl-35-Cl-37 isotopic species. An effective coupling constant xi(39)(c) = 0.1975(2) cm(-1) results from a full rotational analysis of a difference spectrum, obtained by subtracting the (CH2Cl2)-Cl-35 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 I' representation yields a set of accurate effective rotational and distortion constants up to quartic terms for the excited slates of both fundamental bands. The standard deviation of the fit was 0.893 x 10(-3) cm(-1).