Millimeter Wave Fourier Transform Spectroscopy of Laser Photolysis Products

<div> Reactive intermediates and radicals are commonly present in atmospheric, combustion, and astrophysical environments, but their study in the laboratory remains challenging due to their short lifetime and low concentration. Many methods have been used to produce unstable molecules for spectroscopic study, but pulsed laser photolysis is less common with rotational spectroscopy, even though it allows for the study of dynamics as well as spectra. In this study pulsed laser photolysis has been implemented in a new room-temperature flow cell with the Fast Lille Absorption emiSsion High-resolution (FLASH) spectrometer to probe transient and unstable molecular species. High-energy photons (typically 266 nm) break stable molecules creating products with significant internal energy. This energy is sufficient to populate small molecules in excited vibrational states, enabling rotational spectroscopic measurements of the ground and the vibrationally excited states. In addition, dynamics can be monitored in time domain using Fourier transform spectroscopy experiments. In this newly-built setup, we have successfully generated reactive radicals, such as HCO, through the photolysis of appropriate precursors. Additionally, some interesting intermediates, specifically the Criegee intermediate, have also been directly observed through photolytically initiated reactions. The preliminary results from this instrument will be presented with perspectives towards future works. </div>