title: CH radical production from 248 nm photolysis or discharge-jet dissociation of CHBr3 probed by cavity ring-down absorption spectroscopy.
abstract: The A-X bands of the CH radical, produced in a 248 nm two-photon photolysis or in a supersonic jet discharge of CHBr(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(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(3))=(5.0+/-2.5)10(-4) for a photolysis laser fluence of 44 mJ cm(-2) per pulse corresponding to a two-photon process only. In addition, the internal energy distribution of CH(X (2)Pi) has been obtained, and thermalized population distributions have been simulated, leading to an average vibrational temperature T(vib)=1800+/-50 K and a rotational temperature T(rot)=300+/-20 K. An alternative technique for producing the CH radical has been tested using discharge-induced dissociation of CHBr(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.
authors.affiliation: Laboratoire Interuniversitaire des Systèmes Atmosphériques, UMR 7583, Universités Paris VII et XII, 61 Avenue Gal de Gaulle, F-94010 Créteil Cedex, France.
authors.forename: C
authors.initials: C
authors.lastname: Romanzin
authors.forename: S
authors.initials: S
authors.lastname: Boyé-Péronne
authors.forename: D
authors.initials: D
authors.lastname: Gauyacq
authors.forename: Y
authors.initials: Y
authors.lastname: Bénilan
authors.forename: M-C
authors.initials: MC
authors.lastname: Gazeau
authors.forename: S
authors.initials: S
authors.lastname: Douin