3
Reaction of O( P) with ClONO2
J. Phys. Chem. A, Vol. 102, No. 44, 1998 8563
ClONO2 via reaction 9 such that the rate-limiting step for NO3
formation will be reaction 1. Thus, the measured temporal
profiles of NO3 cannot help distinguish reaction 1a from
reactions 1e and 1g. We indirectly gauged the contribution of
these two channels by varying the ratio of [O3] to [ClONO2].
In this way, the fraction of Cl atoms that reacts with O3, rather
than with ClONO2, will change and alters NO3 production.
Changing the [ClONO2]/[O3] ratio by a factor of ∼10 at 298 K
Therefore, to check for this, pure N2 was used and all the Teflon
tubing was replaced by glass; the intercept did not change. Thus,
we are at a loss to explain this larger intercept. Yet the
agreement between the values of k1 measured in the LPA
apparatus with that measured in the RF apparatus lends
confidence to the measured yields.
This study provides a comprehensive measurement of k1 and
the first report of the direct determination of the products of
reaction 1. However, the previous conclusion regarding the
negligible contribution of reaction 1 to the lower stratospheric
destruction of ClONO2 remains unchanged. As noted in earlier
papers, reaction 1 becomes a significant loss process only at
higher altitudes, where the abundance of ClONO2 is rather low.
(∼2 at 273 K and ∼5 at 248 K), thus changing the fraction of
Cl atoms that reacted with O3 from ∼15% to ∼65% at 298 K
(
∼30 to ∼50% at 273 K and ∼20 to 50%), did not appreciably
affect the measured NO3 yield. Given the large uncertainty in
the values of the yield, we can say that the sum of the branching
ratio for channels 1e and 1g is not very large (<0.3). However,
it appears channels 1e and 1g are less likely than channel 1a
because the measured rate constant and its variation with
temperature are consistent with that for a simple abstraction
reaction.
Acknowledgment. We thank L. G. Huey for the CIMS
analyses of the ClONO2 samples, R. K. Talukdar for instructive
discussion, and M. K. Gilles for help in synthesizing ClONO2.
This work was funded in part from the National Aeronautic
and Space Administration’s Mission to Planet Earth. L.G. thanks
the NASA Global Change Research Program for a doctoral
fellowship, and M.H.H. acknowledges a CIRES Visitor fellow-
ship.
To our knowledge, the yield of NO3 in reaction 1 has not
been measured previously. Our measured yield of NO3 at 298
K was approximately unity. An average of the values shown
in Table 2 would be 1.07 ( 0.36, by taking an average of the
internal and external calibration results. The agreement between
the values obtained using ClONO2 photolysis as the internal
standard and N2O5 photolysis as the external standard is good
considering the errors involved. On the basis of these measure-
ments, it appears that NO3 and ClO are the primary products
of this reaction and account for at least 70% of the reaction.
Obviously, we cannot rule out other minor products.
References and Notes
(
1) Yokelson, R. J.; Burkholder, J. B.; Fox, R. W.; Talukdar, R. K.;
Ravishankara, A. R. J. Phys. Chem. 1994, 98, 13144.
2) Burkholder, J. B.; Talukdar, R. K.; Ravishankara, A. R. Geophys.
Res. Lett. 1994, 21, 585-588.
3) Hanson, D. R.; Ravishankara, A. R. J. Geophys. Res. 1991, 96,
(
(
5
081-5090.
(4) Hanson, D. R.; Ravishankara, A. R. J. Geophys. Res. 1991, 96,
1
7307-17314.
Smith et al.12 hypothesized that reaction 1 produced O2 and
(5) Yokelson, R. J.; Burkholder, J. B.; Goldfarb, L.; Fox, R. W.; Gilles,
M. K.; Ravishankara, A. R. J. Phys. Chem. 1995, 99, 13976-13983.
ClONO to account for the production of Cl2, O2, and N2O5 in
the 302.5 nm photolysis of ClONO2. They suggested that the
photolysis of ClONO2 produced O atoms and that the subsequent
reactions of the O atoms led to these products. However, we
now know that the quantum yield for the production of O atoms
in the photolysis of ClONO2 around 300 nm is <10% and that
(6) Yokelson, R. L.; Burkholder, J. B.; Ravishankara, A. R. J. Phys.
Chem. 1997, 101, 6667-6678.
(7) Goldfarb, L.; Schmoltner, A.-M.; Gilles, M. K.; Burkholder, J. B.;
Ravishankara, A. R. J. Phys. Chem. 1997, 101, 6658-6666.
(8) DeMore, W. B.; Sander, S. P.; Golden, D. M.; Hampson, R. F.;
Kurylo, M. J.; Howard, C. J.; Ravishankara, A. R.; Kolb, C. E.; Molina,
M. J. Chemical Kinetics and Photochemical Data for Use in Stratospheric
Modeling, EValuation No. 12; Jet Propulsion Laboratory: Pasadena, Calif.,
1997.
the major products are Cl + NO3 and ClO + NO2, with the
former set being the major products.7
,6,16,17
The subsequent
(
9) Molina, L. T.; Spencer, J. E.; Molina, M. J. Chem. Phys. Lett. 1977,
reactions of Cl with ClONO2 and the reaction of NO3 with NO2
either generated by photolysis or decomposition of ClONO2)
4
5, 158-162.
(
(10) Kurylo, M. J. Chem. Phys. Lett. 1977, 49, 467-470.
(
11) Adler-Golden, S. M.; Wiesenfeld, J. R. Chem. Phys. Lett. 1981,
would lead to the products observed by Smith et al. In the
absence of the details of the experiments of Smith et al., it is
difficult to say if their observed products could be quantitatively
accounted for by the photochemistry in ClONO2 around 300
nm that is now reasonably well understood. However, it is clear
that generation of ClO and NO3 from reaction 1 is not contrary
to the end products observed by Smith et al.
8
1
2
2, 281-284.
(
12) Smith, W. S.; Chou, C. C.; Rowland, F. S. Geophys. Res. Lett.
977, 4, 517-519.
(13) Vaghjiani, G. L.; Ravishankara, A. R. Int. J. Chem. Kinet. 1990,
2, 351-358.
(14) Schmeisser, M. Chlorine Nitrate. In Handbook of PreparatiVe
Inorganic Chemistry; Brauer, G., Ed.; Academic: San Diego, CA, 1967; p
326.
(
15) Orkin, V. L.; Huie, R. E.; Kurylo, M. J. J. Phys. Chem. 1996, 100,
It appears that the yield of NO3 is the same at the three
temperatures examined here. The invariance of the yield with
temperature suggests that a majority of the reaction proceeds
via abstraction and that ClO and NO3 are the major products.
8
907-8912.
(16) Moore, T. A.; Okumura, M.; Tagawa, M.; Minton, T. K. Faraday
Discuss. Chem. Soc. 1995, 100, 295-307.
(17) Tyndall, G. S.; Kegley-Owen, C. S.; Orlando, J. J.; Calvert, J. G.
J. Chem. Soc., Faraday Trans. 1997, 93, 2675.
The intercepts in the plots of the first-order rate coefficients
for the loss of O atoms, measured by observing NO3 production,
(
18) Malleson, A. M.; Kellet, H. M.; Myhill, R. G.; Sweetenham, W.
P. FACSIMILE, version 4.0; AEA Technology, Harwell: Oxfordshire, U.K.,
1995.
-1
versus [ClONO2] were too large (∼50-350 s ) to be accounted
for by the known loss processes for O atoms in the absence of
ClONO2. This intercept cannot be measured directly, i.e., in
the absence of ClONO2. Reactions such as 14 and 15 cannot
account for the observed intercepts. If oxygen atoms were
reacting with one or more products of reaction 1, such as NO3,
a larger intercept might be observed. However, on the basis of
the calculated concentrations of the photoproducts, it appears
that secondary reactions were not the cause of this large
intercept. Another possibility for the larger intercept is the
presence of small amounts of reactive species, such as NO2, in
the main flow of N2. NO2 is known to permeate into Teflon.
(
19) Molina, L. T.; Molina, M. J. J. Geophys. Res. 1986, 91, 14501-
4508.
20) Harwood, M. H.; Jones, R. L.; Cox, R. A.; Lutman, E.; Rattigan,
1
(
O. V. J. Photochem. Photobiol. 1993, A73, 167-175.
(21) Harwood, M. H.; Burkholder, J. B.; Ravishankara, A. R. J. Phys.
Chem. 1998, 102, 1309-1317.
(
22) Ravishankara, A. R.; Davis, D. D.; Smith, G.; Tesi, G.; Spencer, J.
Geophys. Res. Lett. 1978, 4, 7-9.
(23) Ravishankara, A. R.; Smith, G.; Watson, R. T.; Davis, D. D. J.
Phys. Chem. 1977, 81, 2220-2225.
(24) Mauldin, R. L., III; Burkholder, J. B.; Ravishankara, A. R. J. Phys.
Chem. 1992, 96, 2582-2588.
25) Atkinson, R.; Baulch, D. L.; Cox, R. A.; Hampson, R. F.; Kerr, J.
A.; Troe, J. J. Phys. Chem. Ref. Data 1992, 21, 1125-1568.
(