Analysis of FTIR spectra of CH₂⁷⁹Br³⁵Cl; the ν₃ and ν₉ fundamentals

Abstract

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.