Jet-cooled radical spectroscopy using a color center laser
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Jet-cooled radical spectroscopy has been developed for its potential application to high resolution infrared spectroscopic studies of large radicals. In general, radicals containing more than three atoms heavier than hydrogen can not be studied in a room temperature cell using high resolution techniques. For such large species, the infrared spectrum becomes congested and unresolvably complex because of the presence of overlapping rotational lines and vibrational hot bands. By cooling radicals in a supersonic expansion, excited rotational and vibrational levels are depopulated, giving simplified spectrum.
In this technique, radicals are produced inside a slit supersonic nozzle by 193 or 248 nm excimer laser photolysis of a gas mixture consisting of 1% suitable precursor seeded into 1-11 atm carrier gas (typically helium). To reduce the vibrational temperature of the hot radicals produced upon photolysis, the radicals are thermalized by collisions with the room temperature helium inside the slit thermalization region before expansion. The radicals are then cooled rotationally in the subsequent expansion, and their transient absorption is probed downstream of the slit orifice by a tunable, computer-controlled color center laser.
The jet-cooled infrared spectroscopy technique was first tested on small radicals with known high resolution spectra. Small radicals such as NH
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Richnow, Marilyn Lea. "Jet-cooled radical spectroscopy using a color center laser." (1990) Diss., Rice University. https://hdl.handle.net/1911/16385.