Randall, C.J., Murray, C., and McKendrick, K.G. (2000) State-specific collisional coupling of the CH A 2Δ and B 2Σ- states. Physical Chemistry Chemical Physics, 2 (4). pp. 461-471. ISSN 1463-9076 (doi:10.1039/a908494k)
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Publisher's URL: http://dx.doi.org/10.1039/a908494k
Electronically excited CH radicals have been prepared in chosen vibrational levels of the A 2Δ and B 2Σ− states by selective laser excitation. The evolution of the populations in the initial and collisionally produced vibronic levels has been followed by time- and wavelength-resolved fluorescence spectroscopy. It is found that CO2, as a model collision partner, efficiently promotes the coupling of the A 2Δ and B 2Σ− states at room temperature (∽295 K). CH A 2Δ, v=1 is reversibly transferred to the near-degenerate B 2Σ−, v=0 level, and irreversibly vibrationally relaxed to A 2Δ, v=0, with comparable probabilities for these competing processes. CH B 2Σ−, v=0 is correspondingly reversibly transferred to A 2Δ, v=1 and irreversibly transferred to A 2Δ, v=0. The branching ratio for these two product vibrational states is ca. 2:1, which contrasts markedly with the predictions of energy-gap scaling laws. The A 2Δ, v=0 level is found to be only weakly quenched by CO2, in agreement with previous measurements. These observations have important consequences for the use of laser-induced fluorescence spectroscopy as a tool for monitoring the density of CH in collisional environments, and in the interpretation of previously measured quenching rate constants for electronically excited CH.
|Glasgow Author(s):||Murray, Dr Craig|
|Authors:||Randall, C.J., Murray, C., and McKendrick, K.G.|
|College/School:||College of Science and Engineering > School of Chemistry|
|Journal Name:||Physical Chemistry Chemical Physics|
|Journal Abbr.:||Phys. Chem. Chem. Phys.|
|Published Online:||7 January 2000|