Intense, hyperthermal source of organic radicals for matrix-isolation spectroscopy
We have incorporated a pulsed, hyperthermal nozzle with a cryostat to study the matrix-isolated infrared spectroscopy of organic radicals. The radicals are produced by pyrolysis in a heated, narrow-bore (1-mm-diam) SiC tube and then expanded into the cryostat vacuum chamber. The combination of high nozzle temperature (up to 1800 K) and near-sonic flow velocities (on the order of 104?cm?s?1) through the length of the 2 cm tube allows for high yield of radicals (approximately 1013?radicals?pulse?1) and low residence time (on the order of 10 ?s) in the nozzle. We have used this hyperthermal nozzle/matrix isolation experiment to observe the IR spectra of complex radicals such as allyl radical (CH2CHCH2), phenyl radical (C6H5), and methylperoxyl radical (CH3OO). IR spectra of samples produced with a hyperthermal nozzle are remarkably clean and relatively free of interfering radical chemistry. By monitoring the unimolecular thermal decomposition of allyl ethyl ether in the nozzle using matrix IR spectroscopy, we have derived the residence time (?nozzle) of the gas pulse in the nozzle to be around 30 ?s. © 2003 American Institute of Physics.