CH radical production from 248 nm photolysis or discharge-jet dissociation of CHBr{sub 3} probed by cavity ring-down absorption spectroscopy

Journal Article · Thu Sep 21 04:00:00 EDT 2006 · Journal of Chemical Physics

DOI:https://doi.org/10.1063/1.2333456· OSTI ID:20864293

Romanzin, C; Boye-Peronne, S; Gauyacq, D; Benilan, Y; Gazeau, M -C; Douin, S ^[1]

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1. Laboratoire Interuniversitaire des Systemes Atmospheriques, UMR 7583, Universites Paris VII et XII, 61 Avenue Gal de Gaulle, F-94010 Creteil Cedex (France)

The A-X bands of the CH radical, produced in a 248 nm two-photon photolysis or in a supersonic jet discharge of CHBr{sub 3}, have been observed via cavity ring-down absorption spectroscopy. Bromoform is a well-known photolytic source of CH radicals, though no quantitative measurement of the CH production efficiency has yet been reported. The aim of the present work is to quantify the CH production from both photolysis and discharge of CHBr{sub 3}. In the case of photolysis, the range of pressure and laser fluences was carefully chosen to avoid postphotolysis reactions with the highly reactive CH radical. The CH production efficiency at 248 nm has been measured to be {phi}=N(CH)/N(CHBr{sub 3})=(5.0{+-}2.5)10{sup -4} for a photolysis laser fluence of 44 mJ cm{sup -2} per pulse corresponding to a two-photon process only. In addition, the internal energy distribution of CH(X {sup 2}{pi}) has been obtained, and thermalized population distributions have been simulated, leading to an average vibrational temperature T{sub vib}=1800{+-}50 K and a rotational temperature T{sub rot}=300{+-}20 K. An alternative technique for producing the CH radical has been tested using discharge-induced dissociation of CHBr{sub 3} in a supersonic expansion. The CH product was analyzed using the same cavity ring-down spectroscopy setup. The production of CH by discharge appears to be as efficient as the photolysis technique and leads to rotationally relaxed radicals.

• OSTI ID: 20864293
• Journal Information: Journal of Chemical Physics, Journal Name: Journal of Chemical Physics Journal Issue: 11 Vol. 125; ISSN JCPSA6; ISSN 0021-9606
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
ABSORPTION SPECTROSCOPY
BROMOFORM
DISSOCIATION
ENERGY SPECTRA
MULTI-PHOTON PROCESSES
PHOTOLYSIS
PHOTONS
RADICALS
ROTATIONAL STATES
VIBRATIONAL STATES