Time-Resolved Fourier-Transform Millimeter-Wave Spectroscopy of the Simplest Criegee Intermediate, CH2OO, in Its ν7 = 1 State.

In the present work, we have investigated the rotational spectrum of the ν7 = 1 vibrational state of CH2OO in the 250-500 GHz range, produced by photolysis of the CH2I2 precursor in the presence of O2. In order to carry out such an investigation, we have developed a new experimental setup that combines UV pulsed laser photolysis and a room-temperature flow cell with a Fourier-transform millimeter-wave emission spectrometer. A multiple-pulse acquisition protocol enables time-resolved detection of transient species over millisecond time scales to improve signal-to-noise ratios through averaging. This system enables in situ observation of transient species and their vibrationally excited states under thermal conditions, demonstrating the capabilities of a new instrument that can record time-resolved rotational spectra. A total of 120 transitions were measured and used to determine accurate spectroscopic parameters for CH2OO (ν7 = 1).