Oxygen Atom Recombination

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32nd 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, D.V. Lopaev,
T.V. Rakhimova Skobeltsyn Institute of Nuclear
Physics, Moscow State University, Russia
Michael Heaven Department of Chemistry Emory
University, USA
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The Pure Oxygen Kinetics (POK)
O atom formation O2 h? (lt242 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
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Whats 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 ?36)
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(a1?)
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(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.
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The fate of O3(v)
O3(?) formation   1. O(3P) O2 M ?
O3(?) M
O3(?) destruction 2. O3(?) O2(1?) ?
O(3P) 2O2 4a. O3(?) O(3P) ? 2 O2 5. O3(?) X
? products 
O3(?) stabilization   3. O3(?) M ? O3
M (O2, N2) 4b. O3(?) O(3P) ? O3 O(3P) 6.
O3(?) ? O3 h?
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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 ONO 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.

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Experimental setup
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)
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Details of the flow cell
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Schematic view of time-resolved absorption
spectroscopy for O3 concentration measurements
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Temporal profiles of O2(a1?) emission after laser
photolysis of O3 with different buffer gases
PO31 Torr E 87 mJ cm-2 T300 K.
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Temporal profiles of O2(a1?) emission after laser
photolysis of O2/O3/He mixture model predictions
PO2460 Torr PO31 Torr, E87 mJ cm-2, T300
K. PHe varied 0 244 Torr
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Temporal profiles of O2(a1?) emission after laser
photolysis of O2/O3/CO2 mixture model
predictions
PO2460 Torr PO31 Torr, E87 mJ cm-2, T300
K. PCO2 varied 0 97 Torr.
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O Atom removal in O3/O2 photochemistry
ONOM?NO2M, 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.
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O3 recovery in O3/O2/Ar/CO2 photochemistry
a)
O3 density temporal profiles at E90 mJ/cm2,
total gas pressure Ptot 706 Torr, gas
temperature T300 K for several O2 pressure.
O3 density temporal profiles at E90 mJ/cm2,
total gas pressure Ptot 712 Torr, PO2 235 Torr,
gas temperature T300 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
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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 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.
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The ratio of the rate of O2(1?) removal in the
process (2) to the rate of the process (13)
Atmospheric applications

• O3(??2) O2(1?) ? O(3P) 2O2 k25.210-11 cm3/s
• 13) O2(1?) O2(X) ? O2(X) O2(X) k133.010-18
  cm3/s

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The fraction of O3(v) that dissociates in the
processes (1) and (4a)
Atmospheric applications
2) O3(??2) O2(1?) ? O(3P) 2O2 k15.210-11
cm3/s 4) O3(?) O(3P) ? O3
O(3P) k41.510-11 cm3/s 4a) O3(?) O(3P) ? 2
O2 k4a4.510-12 cm3/s
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A systematic error caused by reaction O3(v)
O2(1?) ? O(3P) 2O2
Measurement errors of the rate constant of
process OO2M? O3M
A systematic error caused by reaction O3(v) O
(3P) ? 2 O2
At O2(a)0.9?O?31016 cm-3 O22.11019 cm-3
?20.58, ?4a0.14.
Klais et al. (Int. J. Chem. Kinet. 12, 469-490
(1980)) experiments T219 K, O24.4?1017 cm-3,
O1015 cm-3 ?4a 0.22.
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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.