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 (6) 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 m) 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 (6) band. Rotational parameters A, B, and C and higher-order parameters (J), (JK), (K), (J), and (K) were determined precisely. Rotational perturbations for K-a = 3, K-a = 6, and K-a 11 on high-J levels were observed. In particular, for K-a = 6, frequency shifts as a function of J showed an avoided crossing; the shifts were analyzed in terms of a Coriolis interaction between modes (6) and (8) of CH2OO. According to the distinct temporal profiles, lines of a hot band near 899.5 cm(-1) were also identified.