Infrared absorption of gaseous CH₂BrOO detected with a step-scan Fourier-transform absorption spectrometer

CH₂BrOO radicals were produced upon irradiation, with an excimer laser at 248 nm, of a flowing mixture of CH₂Br₂ and O₂. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record temporally resolved infrared (IR) absorption spectra of reaction intermediates. Transient absorption with origins at 1276.1, 1088.3, 961.0, and 884.9 cm^-1 are assigned to ν₄ (CH₂-wagging), ν₆ (O-O stretching), ν₇ (CH₂-rocking mixed with C-O stretching), and ν₈ (C-O stretching mixed with CH₂-rocking) modes of syn-CH₂BrOO, respectively. The assignments were made according to the expected photochemistry and a comparison of observed vibrational wavenumbers, relative IR intensities, and rotational contours with those predicted with the B3LYP/aug-cc-pVTZ method. The rotational contours of ν₇ and ν₈ indicate that hot bands involving the torsional (ν₁₂) mode are also present, with transitions 70112vv and 80112vv, v = 1-10. The most intense band (ν₄) of anti-CH₂BrOO near 1277 cm^-1 might have a small contribution to the observed spectra. Our work provides information for directly probing gaseous CH₂BrOO with IR spectroscopy, in either the atmosphere or laboratory experiments.