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High-resolution vibration-rotational spectra and rotational perturbation of the OO-stretching (ν6) band of CH2OO between 879.5 and 932.0 cm-1.

We report the observation of a rotationally resolved ν6 band associated with the OO-stretching mode of the simplest Criegee intermediate, CH2OO, in the range of 879.5-932.0 cm-1 (11.37-10.73 μm) at an optical resolution of 0.0015 cm-1. The spectra were recorded with a tunable cw external-cavity quantum-cascade laser (EC-QCL) system coupled with a Herriott multipass absorption cell. Over one thousand lines were assigned to determine the rovibrational parameters of the ν6 band. Rotational parameters A', B', and C' and higher-order parameters ΔJ, ΔJK, ΔK, δJ, and δK were determined precisely. Rotational perturbations for Ka' = 3, Ka' = 6, and Ka' ≥ 11 on high-J levels were observed. In particular, for Ka' = 6, frequency shifts as a function of J' showed an avoided crossing; the shifts were analyzed in terms of a Coriolis interaction between modes ν6 and ν8 of CH2OO. According to the distinct temporal profiles, lines of a hot band near 899.5 cm-1 were also identified.