R. Curl, K.K. Murray, M. Petri, M. Richnow, F. Tittel, Infrared spectroscopy of jet-cooled transient molecules, Chem. Phys. Lett., 161 (1989) 98-102; doi: 10.1016/0009-2614(89)85038-9
Free radicals are produced by excimer laser flash photolysis of a suitable precursor inside the nozzle of a pulsed slit jet and cooled by supersonic expansion from the slit. The infrared spectra of the radicals are then probed by a single-frequency color-center laser. This technique has been tested on the NH2 radical.