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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 , - PowerPoint PPT Presentation
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Oxygen Atom Recombination in the Presence of Singlet
Molecular Oxygen
Michael HeavenDepartment of Chemistry
Emory University, USA
Valeriy AzyazovP.N. Lebedev Physical Instituteof RAS, Samara Branch, Russia
32nd 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
The Pure Oxygen Kinetics (POK)
O atom formationO2 + 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
What’s missing in the POK?
M.J. Kurylo, et al., M.J. Kurylo, et al., J. PhotochemJ. Photochem. . 33, 71 (1974), 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 3820.W.T. Rawlins W.T. Rawlins et alet al.. J. Chem. Phys., J. Chem. Phys., 8787, 5209 (1987), 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 V.N. Azyazov et alet al. Chem. Rhys. Lett., . Chem. Rhys. Lett., 482482, 56 (2009), 56 (2009) observed fast quenching of O2(a1Δ) in the O/O3/O2 system. G.A. West G.A. West et alet al. , Chem. Phys. Lett., 56, 429 (1978) . , Chem. Phys. Lett., 56, 429 (1978) observed that vibrationally excited ozone reacts effectively with oxygen atom.
1) Ozone molecule formed in recombination processO + O2 + M O3(v) + M
is vibrationally excited!W.T Rawlins W.T Rawlins et alet al. J. Geophys. Res., . J. Geophys. Res., 8686, 5247 (1981), 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(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
Present work
(1) 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.
(2) 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.
Experimental setupExperimental setupO2/O3/buffer
To pump
248 nm
Power meter
1268 nm filter
Ge photo detector
OO33 + + hh (248 nm) (248 nm) O(O(11D) D) + + OO22(a(a11)),, 0.90.9 O(O(33P) + OP) + O22((
33) ) O(O(11D)D) + O + O22 O(O(33P) + P) + OO22(b(b
11)) OO22(a(a11) ) OO22((
33)+ )+ hh (1268 nm) (1268 nm)
7
Details of the flow cell
8
Schematic view of time-resolved absorption spectroscopy for O3
concentration measurements
LED
Monoch-romator
258 nm
PMT
О2/О3/М
Laser beam
Supply fiber
Withdraw fiber
Temporal profiles of OTemporal profiles of O22(a(a11ΔΔ) emission after laser ) emission after laser photolysis of Ophotolysis of O3 3 with different buffer gaseswith different buffer gases
PO3=1 Torr
E =87 mJ cm-2
T=300 K.
Temporal profiles of OTemporal profiles of O22(a(a11ΔΔ) emission ) emission after laser photolysis of Oafter laser photolysis of O22/O/O33/He /He
mixture + model predictionsmixture + model predictions
PO2=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 OTemporal profiles of O22(a(a11ΔΔ) ) emission after laser photolysis of emission after laser photolysis of
OO22/O/O33/CO/CO22 mixture + model mixture + model predictionspredictions
O Atom removal in OO Atom removal in O33/O/O22 photochemistryphotochemistry
O+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.
OO33 recovery in O recovery in O33/O/O22/Ar/CO/Ar/CO22 photochemistryphotochemistry
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
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)
Observations
(1)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 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 sec against 13 sec predicted by POK. Oxygen atoms regenerate in the process O2(1) + 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) 2) O3(υ2) + O2(1) O(3P) +2O2 k2=5.2×10-11 cm3/s13) O2(1∆) +O2(X) O2(X) + O2(X) k13=3.0×10-18 cm3/s
2 3 2
13 2 2
[O ( 2)][O ( )]
[O ][O ( )]
k a
Rk a
M
2 1Δ M
13 2 2 3 4 υ
k k [O][M]R =
k k [O (a)]+k [M]+k [O]+A
Atmospheric applications
The fraction of O3(v) that dissociates in the processes (1) and (4a)
2) O3(υ2) + O2(1) O(3P) +2O2 k1=5.2×10-11 cm3/s4) O3(υ) + O(3P) O3 + O(3P) k4=1.5×10-11 cm3/s4a) O3(υ) + O(3P) 2 O2 k4a=4.5×10-12 cm3/s
3loss
3
O (v) dissociation rate
O (v) stabilization rateR
4a 2 2
loss M2 2 3 4 υ
k [O]+k [O (a)]R =
k [O (a)]+k [M]+k [O]+A
Atmospheric applications
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
1M3
2 2 3 4 M2 M
1 2 2 2 2 2M
k [M]k [O (a)][O ( 2)] k [O]
1k [O][O ][M] k [O (a)] k [O (a)]
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.
-1 -1
3 34a 3 4 M M
4a1 2 4a 4a 4a
M
k [M] k [M]k [O][O (υ 2)] k
= = + 3+k [O][O ][M] k k [O] k [O]
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.
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.