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

2. The Pure Oxygen Kinetics (POK) O atom formationO 2 + h (<242 nm)  O + O Ozone formation O + O 2 + M  O 3 + M O 3 photolysisO 3 + h (  320 nm)  O 2 (a) + O( 1 D)  O 2 (X) + O( 3 P) Odd oxygen removalO + O 3  O 2 + O 2 O + O + M  O 2 + M O 2 (a 1 ∆) deactivationO 2 (a 1 ∆)  O 2 (X) +h (1268 nm) O 2 (a 1 ∆) +O 2 (X)  O 2 (X) + O 2 (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? M.J. Kurylo, et al., J. Photochem. 3, 71 (1974) M.J. Kurylo, et al., J. Photochem. 3, 71 (1974) found that the rate constant for O 2 (a 1 Δ) quenching by O 3 ( ) 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) W.T. Rawlins et al. J. Chem. Phys., 87, 5209 (1987) estimated that the rate constant for quenching of O 2 (a 1  ) by ozone with two or more quanta of the stretching modes excited to be in the range 10 -11 -10 -10 cm 3 s -1. V.N. Azyazov et al. Chem. Rhys. Lett., 482, 56 (2009) V.N. Azyazov et al. Chem. Rhys. Lett., 482, 56 (2009) observed fast quenching of O 2 (a 1 Δ) in the O/O 3 /O 2 system. G.A. West et al., Chem. Phys. Lett., 56, 429 (1978) G.A. West et al., Chem. Phys. Lett., 56, 429 (1978) observed that vibrationally excited ozone reacts effectively with oxygen atom. 1)Ozone molecule formed in recombination process O + O 2 + M  O 3 (v) + M is vibrationally excited! W.T Rawlins et al. J. Geophys. Res., 86, 5247 (1981) 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) O 3 (v) has a high reactivity!

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

5. Present work (1) The rates of O 2 (a 1 ∆) removal, O atom recom- bination and O 3 recovery were measured in the O/O 2 (a 1 ∆)/O 2 /O 3 system using laser - pulse technique, time-resolved emission/absorption spectroscopy and O+NO chemiluminescent reaction. (2) New experimental data showing that vibrationally excited ozone is effectively quenched by O 2 (a 1 ∆) molecule and O atom are reported. The contribution of these quenching channel on the O 2 (a 1 ∆) and O 3 budgets in the middle atmosphere and oxygen-containing plasma is discussed.

6. Experimental setup O 2 /O 3 /buffer To pump 248 nm Power meter 1268 nm filter Ge photo detector O 3 + h (248 nm)  O( 1 D) + O 2 (a 1  ),    0.9  O( 3 P) + O 2 ( 3  )  O( 3 P) + O 2 ( 3  ) O( 1 D) + O 2  O( 3 P) + O 2 (b 1  ) O 2 (a 1  )  O 2 ( 3  )+ h (1268 nm)

7. 7 Details of the flow cell

8. 8 Schematic view of time-resolved absorption spectroscopy for O 3 concentration measurements LED Monoch- romator 258 nm PMT О2/О3/МО2/О3/М Laser beam Supply fiber Withdraw fiber

9. Temporal profiles of O 2 (a 1 Δ) emission after laser photolysis of O 3 with different buffer gases P O3 =1 Torr E =87 mJ cm -2 T=300 K.

10. Temporal profiles of O 2 (a 1 Δ) emission after laser photolysis of O 2 /O 3 /He mixture + model predictions P O2 =460 Torr P O3 =1 Torr, E=87 mJ cm -2, T=300 K. P He varied: 0 – 244 Torr

11. P O2 =460 Torr P O3 =1 Torr, E=87 mJ cm -2, T=300 K. P CO2 varied: 0 – 97 Torr. Temporal profiles of O 2 (a 1 Δ) emission after laser photolysis of O 2 /O 3 /CO 2 mixture + model predictions

12. O Atom removal in O 3 /O 2 photochemistry O+NO+M  NO 2 *+M, Trace [NO] used for detection Model without O atom regeneration from secondary reactions of O 3 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. O 3 recovery in O 3 /O 2 /Ar/CO 2 photochemistry O 3 density temporal profiles at E=90 mJ/cm 2, total gas pressure P tot =712 Torr, P O2 =235 Torr, gas temperature T=300 K for several CO 2 pressure. The degree of O 3 recovery depends on gas composition while the POK model predicts a full recovery of the ozone at our experimental conditions O 3 density temporal profiles at E=90 mJ/cm 2, total gas pressure P tot =706 Torr, gas temperature T=300 K for several O 2 pressure. a)

14. Observations (1)The degree of O 3 recovery depends on gas composition and for O 3 /O 2 /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 + O 3 (v) – O 2 + O 2 (2) The O 3 recovery time depends also on gas composition and for O 3 /O 2 /Ar mixtures and for the lower curves it is about 50  sec against 13  sec predicted by POK. Oxygen atoms regenerate in the process O 2 ( 1  ) + O 3 (v) – O + O 2 + O 2 (3) Ar quenches O 3 (v) worse than CO 2 or O 2. Replacement of Ar by CO 2 or O 2 results in increasing both the degree and the rate of O 3 recovery.

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

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

17. A systematic error caused by reaction O 3 (v) + O 2 ( 1  )  O( 3 P) +2O 2 Measurement errors of the rate constant of process O+O 2 +M  O 3 +M A systematic error caused by reaction O 3 (v) + O ( 3 P)  2 O 2 At [O 2 (a)]≈0.9  [O]  3×10 16 cm -3 [O 2 ]=2.1×10 19 cm -3 –  2 =0.58,  4a =0.14. Klais et al. (Int. J. Chem. Kinet. 12, 469-490 (1980)) experiments T=219 K, [O 2 ]=4.4  10 17 cm -3, [O]≈10 15 cm -3  4a = 0.22.

18. Conclusions 1. O 3 (v) is a significant quenching agent of O 2 (a 1  ) in the O/O 2 /O 3 systems. 2. Odd oxygen is effectively removed in the process O + O 3 (v)  O 2 + O 2. 3. Processes involving active oxygen species effect significantly on the balance of O 2 (a 1  ) and O 3 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/O 2 /O 3 systems.