Production of Free Radicals

Free radicals have been at the center of the research in our high-resolution spectroscopy lab. In our room-temperature cavity ring-down (CRD) spectroscopy investigations, free radicals are usually produced by UV laser photolysis of judiciously selected precursors, often followed by free-radical reactions. Generating free radicals under jet-cooled conditions is more challenging because producing free radicals by photolysis is not applicable in this case: The pulse duration of the photolysis lasers, either Nd:YAG lasers or excimer lasers, is about 10 ns, while the photolysis beam needs to be focused along the downstream direction to a couple of millimeters. The transit time, viz, the time for the produced free radicals to interact with the CRD laser, is therefore limited to a couple of microseconds, much lower than the ring-down time. In a supersonic jet expansion, free radicals are usually generated using discharge or pyrolysis. These radicals are usually produced in supersonic jet expansion from judiciously selected precursors. Several production methods are applied.

1. Laser photolysis

2. Pulsed discharge

Slit-Jet Discharge Nozzle

3. Laser ablation/vaporization followed by chemical reactions

4. Heated nozzle