Photodissociation dynamics of OClO

Davis, H. Floyd; Lee, Yuan T.
November 1996
Journal of Chemical Physics;11/8/1996, Vol. 105 Issue 18, p8142
Academic Journal
Photofragment translational energy spectroscopy was used to study the dissociation dynamics of a range of electronically excited OClO(A 2A2) vibrational states. For all levels studied, corresponding to OClO(A 2A2←X 2B1) excitation wavelengths between 350 and 475 nm, the dominant product (>=96%) was ClO(2Π)+O(3P). We also observed production of Cl+O2 with a quantum yield of up to 3.9±0.8% near 404 nm, decreasing at longer and shorter wavelengths. The branching ratios between the two channels were dependent on the OClO(A 2A2) excited state vibrational mode. The Cl+O2 yield was enhanced slightly by exciting A 2A2 levels having symmetric stretching+bending, but diminished by as much as a factor of 10 for neighboring peaks associated with symmetric stretching+asymmetric stretching. Mode specificity was also observed in the vibrationally state resolved translational energy distributions for the dominant ClO(2Π)+O(3P) channel. The photochemical dynamics of OClO possesses two energy regimes with distinctly different dynamics observed for excitation energies above and below ∼3.1 eV (λ∼400 nm). At excitation energies below 3.1 eV (λ>=400 nm), nearly all energetically accessible ClO vibrational energy levels were populated, and the minor Cl+O2 channel was observed. Although at least 20% of the O2 product is formed in the ground (X 3Σ-g) state, most O2 is electronically excited (a 1Δg). At E<3.1 eV, both dissociation channels occur by an indirect mechanism involving two nearby excited states, 2A1 and 2B2. Long dissociation time scales and significant parent bending before dissociation led to nearly isotropic polarization angular distributions (β∼0). At excitation energies above 3.1 eV (λ<400 nm), the Cl+O2 yield began to decrease sharply, with this channel becoming negligible at λ<370 nm. At these higher excitation energies, the ClO product was formed with relatively little vibrational energy and...


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