Infrared absorption of gaseous CH3OO detected with a step-scan Fourier-transform spectrometer

Abstract

CH3OO radicals were produced upon irradiation of a flowing mixture of CH3I and O-2 with a KrF excimer laser at 248 nm. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record temporally resolved IR absorption spectra of reaction intermediates. Transient absorption bands with origins at 3033, 2954, 1453, 1408, 1183, 1117, 3020, and 1441 cm(-1) are assigned to nu(1)-nu(6), nu(9), and nu(10) modes of CH3OO, respectively, close to wavenumbers reported for CH3OO isolated in solid Ar. Calculations with density-functional theory (B3LYP/aug-cc-pVTZ) predicted the geometry and the vibrational wavenumbers of CH3OO; the vibrational wavenumbers and relative IR intensities of CH3OO agree satisfactorily with these observed features. The rotational contours of IR spectra of CH3OO, simulated based on ratios of predicted rotational parameters for the upper and lower states and on experimental rotational parameters of the ground state, agree satisfactorily with experimental results; the mixing ratios of a-, b-, and c-types of rotational structures were evaluated based on the direction of dipole derivatives predicted quantum chemically. A feature at 995 cm(-1), ascribed to CH3OOI from a secondary reaction of CH3OO with I, was also observed. (c) 2007 American Institute of Physics.