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Author Zagidullin, M. V. ♦ Pershin, A. A. ♦ Azyazov, V. N. ♦ Mebel, A. M.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY ♦ COMPARATIVE EVALUATIONS ♦ COUPLING ♦ DIPOLE MOMENTS ♦ ELECTRONIC STRUCTURE ♦ EXCITATION ♦ LIQUIDS ♦ LUMINESCENCE ♦ MOLECULE COLLISIONS ♦ MOLECULES ♦ MONOMERS ♦ OXYGEN ♦ POTENTIAL ENERGY ♦ REACTION KINETICS ♦ SPIN ♦ STATISTICAL MODELS ♦ TEMPERATURE DEPENDENCE ♦ TEMPERATURE RANGE 0065-0273 K ♦ TEMPERATURE RANGE 0273-0400 K
Abstract Experimental and theoretical studies of collision induced emission of singlet oxygen molecules O{sub 2}(a{sup 1}Δ{sub g}) in the visible range have been performed. The rate constants, half-widths, and position of peaks for the emission bands of the (O{sub 2}(a{sup 1}Δ{sub g})){sub 2} collisional complex centered around 634 nm (2) and 703 nm (3) have been measured in the temperature range of 90–315 K using a flow-tube apparatus that utilized a gas-liquid chemical singlet oxygen generator. The absolute values of the spontaneous emission rate constants k{sub 2} and k{sub 3} are found to be similar, with the k{sub 3}/k{sub 2} ratio monotonically decreasing from 1.1 at 300 K to 0.96 at 90 K. k{sub 2} slowly decreases with decreasing temperature but a sharp increase in its values is measured below 100 K. The experimental results were rationalized in terms of ab initio calculations of the ground and excited potential energy and transition dipole moment surfaces of singlet electronic states of the (O{sub 2}){sub 2} dimole, which were utilized to compute rate constants k{sub 2} and k{sub 3} within a statistical model. The best theoretical results reproduced experimental rate constants with the accuracy of under 40% and correctly described the observed temperature dependence. The main contribution to emission process (2), which does not involve vibrational excitation of O{sub 2} molecules at the ground electronic level, comes from the spin- and symmetry-allowed 1{sup 1}A{sub g}←{sup 1}B{sub 3u} transition in the rectangular H configuration of the dimole. Alternatively, emission process (3), in which one of the monomers becomes vibrationally excited in the ground electronic state, is found to be predominantly due to the vibronically allowed 1{sup 1}A{sub g}←2{sup 1}A{sub g} transition induced by the asymmetric O–O stretch vibration in the collisional complex. The strong vibronic coupling between nearly degenerate excited singlet states of the dimole makes the intensities of vibronically and symmetry-allowed transitions comparable and hence the rate constants k{sub 2} and k{sub 3} close to one another.
ISSN 00219606
Educational Use Research
Learning Resource Type Article
Publisher Date 2015-12-28
Publisher Place United States
Journal Journal of Chemical Physics
Volume Number 143
Issue Number 24


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