Oxygen Atom Recombination in the Presence of Singlet Molecular Oxygen
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Oxygen Atom Recombination in the Presence of Singlet Molecular Oxygen Michael HeavenDepartment of ChemistryEmory University, USAValeriy AzyazovP.N. Lebedev Physical Instituteof RAS, Samara Branch, Russia 32nd International Symposium on Free Radicals, 21-26 July, Potsdam, GermanyA.A. Chukalovsky, K.S. Klopovskiy,D.V. Lopaev, T.V. RakhimovaSkobeltsyn Institute of Nuclear Physics, Moscow State University, Russia
- The Pure Oxygen Kinetics (POK)O atom formationO2 + h (
Whats missing in the POK?M.J. Kurylo, et al., J. Photochem. 3, 71 (1974) found that the rate constant for O2(a1) quenching by O3() that has one quantum of vibrational energy is faster by a factor of 3820.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(a1) 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.Ozone molecule formed in recombination processO + O2 + M O3(v) + Mis 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!
The fate of O3(v) O3() formation 1. O(3P) + O2 + M O3() + M O3() destruction
2. O3() + O2(1) O(3P) +2O24a. O3() + O(3P) 2 O25. O3() + X products O3() stabilization 3. O3() + M O3 + M (O2, N2)4b. O3() + O(3P) O3 + O(3P)6. O3() O3 + h
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.
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)
*Details of the flow cell
*Schematic view of time-resolved absorption spectroscopy for O3 concentration measurements
Temporal profiles of O2(a1) emission after laser photolysis of O3 with different buffer gasesPO3=1 TorrE =87 mJ cm-2 T=300 K.
Temporal profiles of O2(a1) emission after laser photolysis of O2/O3/He mixture + model predictionsPO2=460 Torr PO3=1 Torr, E=87 mJ cm-2, T=300 K.PHe varied:0 244 Torr
PO2=460 Torr PO3=1 Torr, E=87 mJ cm-2, T=300 K.PCO2 varied:0 97 Torr.Temporal profiles of O2(a1) emission after laser photolysis of O2/O3/CO2 mixture + model predictions
O Atom removal in O3/O2 photochemistryO+NO+MNO2*+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.
O3 recovery in O3/O2/Ar/CO2 photochemistryO3 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 O3 density temporal profiles at E=90 mJ/cm2, total gas pressure Ptot =706 Torr, gas temperature T=300 K for several O2 pressure. a)
ObservationsThe 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 processO + 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 50 msec against 13 msec 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.
The ratio of the rate of O2(1) removal in the process (2) to the rate of the process (13) O3(2) + O2(1) O(3P) +2O2 k2=5.210-11 cm3/s13) O2(1) +O2(X) O2(X) + O2(X) k13=3.010-18 cm3/sAtmospheric applications
The fraction of O3(v) that dissociates in the processes (1) and (4a) 2) O3(2) + O2(1) O(3P) +2O2 k1=5.210-11 cm3/s4) O3() + O(3P) O3 + O(3P)k4=1.510-11 cm3/s4a) O3() + O(3P) 2 O2k4a=4.510-12 cm3/s
A systematic error caused by reaction O3(v) + O2(1) O(3P) +2O2Measurement errors of the rate constant of process O+O2+M O3+MA systematic error caused by reaction O3(v) + O (3P) 2 O2At [O2(a)]0.9[O]31016 cm-3 [O2]=2.11019 cm-3 2=0.58, 4a=0.14. Klais et al. (Int. J. Chem. Kinet. 12, 469-490 (1980)) experiments T=219 K, [O2]=4.41017 cm-3, [O]1015 cm-3 4a = 0.22.
Conclusions1. 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 O3at 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.