193 nm photolysis of CHCl3: Probe of the CH product by CRDS |
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Authors: | Claire Romanzin Brenger Gans Stphane Douin Sverine Boy-Pronne Dolors Gauyacq |
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Institution: | aLaboratoire de Photophysique Moléculaire, CNRS UPR 3361, Université Paris-Sud 11, Bâtiment 210, F-91405 Orsay, France |
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Abstract: | The CH radical production induced by 193 nm two-photon photolysis of CHCl3 has been measured for the first time via the cavity ring-down absorption spectroscopy of its A–X bands, using a commercial nanosecond pulsed dye laser. The range of pressure and laser intensity, as well as the time window detection, have been carefully chosen to ensure a constant CH number density during the measurement and to avoid post-photolysis reactivity. Internal energy distribution of the CH(X2II) fragment has been derived from population distribution simulations, leading to an average vibrational temperature Tvib = 1900 ± 50 K and rotational temperature Trot = 300 ± 20 K. Two competing mechanisms can be invoked for the CH production channel: either two-photon absorption via resonant excited states of CHCl3 leading to dissociation of excited CHCl3, or two-photon sequential dissociation via the formation of the vibrationally excited CHCl2 fragment. The latter mechanism is proposed to be the prominent process for CH formation. |
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Keywords: | Pulsed photolysis CHCl3 Chloroform Methylidyne radical Cavity ring-down absorption spectroscopy Trichloromethane CH radical |
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