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Oxygen Atom Recombination in the Presence of Singlet Molecular Oxygen

32 nd International Symposium on Free Radicals, 21-26 July, Potsdam, Germany. Oxygen Atom Recombination in the Presence of Singlet Molecular Oxygen. Valeriy Azyazov P.N. Lebedev Physical Institute of RAS, Samara Branch, Russia. A.A. Chukalovsky , K.S. Klopovskiy ,

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Oxygen Atom Recombination in the Presence of Singlet Molecular Oxygen

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  1. 32nd International Symposium on Free Radicals, 21-26 July, Potsdam, Germany Oxygen Atom Recombination in the Presence of Singlet Molecular Oxygen ValeriyAzyazov P.N. Lebedev Physical Institute of RAS, Samara Branch, Russia A.A. Chukalovsky, K.S. Klopovskiy, D.V. Lopaev, T.V. Rakhimova Skobeltsyn Institute of Nuclear Physics, Moscow State University, Russia Michael Heaven Department of Chemistry Emory University, USA

  2. The Pure Oxygen Kinetics (POK) O atom formation O2 + h (<242 nm) O + O Ozone formation O + O2 + M  O3+ M O3 photolysis O3 + h (320 nm) O2(a) + O(1D)  O2(X) + O(3P) Odd oxygen removal O + O3 O2+ O2 O + O + M  O2+ M O2(a1∆) deactivation O2(a1∆) O2(X) +h (1268 nm) O2(a1∆) +O2(X)  O2(X) + O2(X) G.P. Brasseur, S. Solomon, Aeronomy of the Middle Atmosphere. Chemistry and Physics of the Stratosphere and Mesosphere Series: Atmospheric and Oceanographic Sciences Library, Vol. 32, 2005, Published by Springer, P.O. Box 17, 3300 AA Dordrecht, The Netherlands

  3. What’s missing in the POK? • Ozone molecule formed in recombination process • O + O2 + M  O3(v) + M • is vibrationally excited! W.T Rawlins et al. J. Geophys. Res., 86, 5247 (1981)observed infrared emission originated from high vibrational levels of ozone (up to 3=6) formed during recombination. 2) O3(v) has a high reactivity! M.J. Kurylo, et al., J. Photochem. 3, 71 (1974) found that the rate constant for O2(a1Δ) quenching by O3() that has one quantum of vibrational energy is faster by a factor of 3820. W.T. Rawlins et al. J. Chem. Phys., 87, 5209 (1987)estimated that the rate constant for quenching of O2(a1) by ozone with two or more quanta of the stretching modes excited to be in the range 10-11-10-10 cm3s-1. V.N. Azyazov et al. Chem. Rhys. Lett., 482, 56 (2009)observed fast quenching of O2(a1Δ) in the O/O3/O2 system. G.A. West et al. , Chem. Phys. Lett., 56, 429 (1978) observed that vibrationally excited ozone reacts effectively with oxygen atom.

  4. The fate of O3(v) O3(υ) formation   1. O(3P) + O2 + M  O3(υ) + M O3(υ) destruction 2. O3(υ) + O2(1)  O(3P) +2O2 4a. O3(υ) + O(3P) 2 O2 5. O3(υ) + X products  O3(υ) stabilization 3. O3(υ) + M  O3 + M (O2, N2) 4b. O3(υ) + O(3P) O3 + O(3P) 6. O3(υ) O3 + h

  5. Present work • The rates of O2(a1∆) removal, O atom recom- bination and O3 recovery were measured in the O/O2(a1∆)/O2/O3 system using laser-pulse technique, time-resolved emission/absorption spectroscopy and O+NO chemiluminescent reaction. • New experimental data showing that vibrationally excited ozone is effectively quenched by O2(a1∆) molecule and O atom are reported. The contribution of these quenching channel on the O2(a1∆) and O3 budgets in the middle atmosphere and oxygen-containing plasma is discussed.

  6. Experimental setup O2/O3/buffer Power meter 1268 nm filter 248 nm Ge photo detector To pump O3 + h (248 nm) O(1D)+ O2(a1),hD,O3 = 0.9  O(3P) + O2(3) O(1D) + O2 O(3P) + O2(b1) O2(a1)  O2(3)+ h (1268 nm)

  7. Details of the flow cell 7

  8. Schematic view of time-resolved absorption spectroscopy for O3 concentration measurements О2/О3/М Withdraw fiber Supply fiber Monoch-romator 258 nm PMT LED Laser beam 8

  9. Temporal profiles of O2(a1Δ) emission after laser photolysis of O3 with different buffer gases PO3=1 Torr E =87 mJ cm-2 T=300 K.

  10. Temporal profiles of O2(a1Δ) emission after laser photolysis of O2/O3/He mixture + model predictions PO2=460 Torr PO3=1 Torr, E=87 mJ cm-2, T=300 K. PHe varied: 0 – 244 Torr

  11. Temporal profiles of O2(a1Δ) emission after laser photolysis of O2/O3/CO2 mixture + model predictions PO2=460 Torr PO3=1 Torr, E=87 mJ cm-2, T=300 K. PCO2 varied: 0 – 97 Torr.

  12. O Atom removal in O3/O2 photochemistry O+NO+MNO2*+M, Trace [NO] used for detection Model without O atom regeneration from secondary reactions of O3 does not fit the O atom decay rate. Without O atom regeneration the accepted rate constant must be reduced by a factor of two.

  13. O3 recovery in O3/O2/Ar/CO2 photochemistry a) O3 density temporal profiles at E=90 mJ/cm2, total gas pressure Ptot =706 Torr, gas temperature T=300 K for several O2 pressure. O3 density temporal profiles at E=90 mJ/cm2, total gas pressure Ptot =712 Torr, PO2 =235 Torr, gas temperature T=300 K for several CO2 pressure. The degree of O3 recovery depends on gas composition while the POK model predicts a full recovery of the ozone at our experimental conditions

  14. Observations • The degree of O3 recovery depends on gas composition and for O3/O2/Ar mixtures (the lower curves it amounts to about 70 %). The standard pure oxygen kinetics (POK) predicts that it must be restored to its initial value (100 %) at our experimental conditions. Odd oxygen is removed in the process • O + O3(v) – O2 + O2 (2) The O3 recovery time depends also on gas composition and for O3/O2/Ar mixtures and for the lower curves it is about 50msec against 13msec predicted by POK. Oxygen atoms regenerate in the process O2(1D) + O3(v) – O + O2 + O2 (3) Ar quenches O3(v) worse than CO2 or O2. Replacement of Ar by CO2 or O2 results in increasing both the degree and the rate of O3 recovery.

  15. The ratio of the rate of O2(1) removal in the process (2) to the rate of the process (13) Atmospheric applications • O3(υ2) + O2(1)  O(3P) +2O2 k2=5.2×10-11 cm3/s • 13) O2(1∆) +O2(X)  O2(X) + O2(X)k13=3.0×10-18 cm3/s

  16. The fraction of O3(v) that dissociates in the processes (1) and (4a) Atmospheric applications 2) O3(υ2) + O2(1)  O(3P) +2O2 k1=5.2×10-11 cm3/s 4) O3(υ) + O(3P) O3 + O(3P)k4=1.5×10-11 cm3/s 4a) O3(υ) + O(3P) 2 O2 k4a=4.5×10-12 cm3/s

  17. A systematic error caused by reaction O3(v) + O2(1)  O(3P) +2O2 Measurement errors of the rate constant of process O+O2+M O3+M A systematic error caused by reaction O3(v) + O(3P)  2 O2 At [O2(a)]≈0.9[O]3×1016 cm-3 [O2]=2.1×1019 cm-3 – 2=0.58, 4a=0.14. Klais et al. (Int. J. Chem. Kinet.12, 469-490 (1980)) experiments T=219 K, [O2]=4.41017 cm-3, [O]≈1015 cm-34a = 0.22.

  18. Conclusions 1. O3(v) is a significant quenching agent of O2(a1) in the O/O2/O3 systems. 2. Odd oxygen is effectively removed in the process O + O3(v)  O2 + O2. 3. Processes involving active oxygen species effect significantly on the balance of O2(a1) and O3 at the atmospheric altitudes 80 - 105 km. 4. Processes involving excited oxygen species may make large systematic errors in the measurements of rate constants in the O/O2/O3 systems.

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