New measurements and global analysis of chloromethane in the region from 0 to 1800 cm−1

Abstract New high resolution Fourier transform spectra of pure 12 CH 3 35 Cl and 12 CH 3 37 Cl isotopomers of chloromethane have been recorded in Wuppertal covering the region from 600 to 3800 cm −1 . New rotational transitions within the v 2 =1, v 5 =1, and v 3 =2 states have been measured at Lille. A first global analysis of the lower four band systems of the molecule (700–1800 cm −1 ) is reported. The model was based on an effective Hamiltonian and dipole moment expressed in terms of irreducible tensor operators. A common set of 125 effective hamiltonian parameters (sixth order) has been adjusted to fit simultaneously some 11 000 IR data for each of the isotopomers including 153 mm wave data for 12 CH 3 35 Cl. The assignments involve 12 sets of transitions (6 cold bands, 3 hot bands, and 3 pure rotational systems for 12 CH 3 35 Cl). The standard deviation was on average 0.00014 cm −1 and 175 kHz for the IR and MMW data, respectively. The v 3 = v 6 =1 state was analysed for the first time principally from observed hot band transitions.