Analysis of FTIR spectra of CH2 79Br35Cl; the ν3 and ν9 fundamentals

The infrared spectrum of isotopically pure CH2 79BrCl has been recorded at a resolution of 0.0025 cm−1 and 0.0023 cm−1 (FWHM) in the range 600–1600 cm−1 with a Bruker IFS 120 HR Fourier transform spectrometer in Wuppertal. Here we report the full rotational analysis of the ν3 and ν9 fundamentals of the most abundant species CH2 79Br35Cl . Improved ground state constants, up to quartic terms, have been obtained from ground state combination differences (GSCD) involving transitions of the fundamentals ν3, ν4, ν5 and ν9. Both ν3 and ν9 transitions were fitted to a Watson-type Hamiltonian in the S-reduction, yielding accurate molecular constants for the ν3 and ν9 excited states. Small local perturbations were observed in both bands. Prominent features in the spectra were assigned to the ν3 and ν9 fundamentals of the CH2 79Br37Cl isotopic species and the hot-bands ν3+ν6 − ν6 and ν9+ν6 − ν6 of CH2 79Br35Cl.