8
9
J. A. McCaulley, A. M. Moyle, M. F. Golde, S. M. Anderson and
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S. Dobe, G. Lendway, I. Szilagyi and T. Berces, Int. J. Chem.
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thus predicting a pressure-independent rate constant for the
CF O loss (as observed experimentally). In the same way, the
3
energetics of the CH O ] NO 43 and CF O ] NO 12
3
2
3
2
systems show barrier heights for the exit channel similar to
10 P. Biggs, C. E. Canosa-Mas, J. M. Fracheboud, A. D. Parr, D. E.
Shallcross, R. P. Wayne and F. Caralp, J. Chem. Soc., Faraday
T rans., 1993, 89, 4163.
that of the CH O ] NO reaction and, consequently, exhibit
3
similar kinetic behaviour, i.e. a pressure-dependent rate con-
11 M. R. Berman and M. C. Lin, J. Phys. Chem., 1983, 87, 3933.
12 F. Caralp, M. T. Rayez, W. Forst, C. Bourbon, M. Brioukov and
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13 K. C. Clemitshaw, L. J. Carpenter, S. A. Penkett and M. E.
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14 S. R. Lin, Y. P. Lee and J. B. Nee, J. Chem. Phys., 1988, 88, 171.
15 J. L. Durant Jr., J. Phys. Chem., 1991, 95, 10701.
16 S. Dobe, T. Berces, F. Temps, H. Gg. Wagner and H. Ziemer, ref.
3, p. 775.
stant for the CX O loss.
It is convenient to express the pressure and temperature
3
dependence of k
using an analytical representation which
loss
will easily provide values of this rate constant in the ranges
1È760 Torr and 220È600 K. Such an expression may be
obtained by adding a constant value to the conventional Troe
expression,44
17 L. Elmaimouni, These Lille, 1994.
k (T )[M]
0
k
\ Cst(T ) ]
FMF (T ), [M]N
18 F. Lahmani, C. Lardeux and D. Soldagi, Chem. Phys. L ett., 1983,
loss
c
1 ] k (T )[M]/k (T )
102, 523.
0
=
19 B. S. Agrawalla and D. W. Setser, J. Phys. Chem., 1986, 90, 2450.
20 P. J. Wantuck, R. C. Oldenborg, S. L. Baughum and K. R. Winn,
J. Phys. Chem., 1987, 91, 3253.
where k (T ) \ k298(T /298 K)~n; k (T ) \ k298(T /298 K)~m;
0
0
=
=
F \ exp ([T /C); Cst \ A exp (B/T ) ] D(T /298 K)F. The
c
four parameters Cst(T ), k (T ), k (T ), F (T ) are obtained at
21 K. J. Rensberger, J. B. Je†ries and D. R. Crosley, J. Chem. Phys.,
1989, 90, 2174.
22 E. Silvente, R. C. Richter and A. J. Hynes, J. Chem. Soc., Faraday
T rans., 1997, 93, 2821.
23 I. W. M. Smith, J. Chem. Soc., Faraday T rans., 1997, 93, 3741.
24 V. Daele, G. Laverdet, G. Le Bras and G. Poulet, J. Phys. Chem.,
1995, 99, 1470.
25 H. Oser, D. Walter, N. D. Stothard, O. Grotheer and H. H. Gro-
theer, Chem. Phys. L ett., 1991, 181, 521.
26 C. F. Melius and J. S. Binkley, T wentieth Symposium
(International) on Combustion. The Combustion Institute, Pitts-
burgh, 1984, p. 575; C. F. Melius, in Chemistry and Physics of
Energetic Materials, NATO SAI 309, ed. S. N. Bulusu, Kluwer,
Dordrecht, 1990, p. 21.
27 P. Ho and C. F. Melius, J. Phys. Chem., 1990, 94, 5120.
28 M. D. Allendorf and C. F. Melius, J. Phys. Chem., 1993, 97, 720.
29 GAUSSIAN 94, Revision C.2, M. J. Frisch, G. W. Trucks, H. B.
Schlegel, P. M. W. Gill, B. G. Johnson, M. A. Robb, J. R. Cheese-
man, T. Keith, G. A. Peterson, J. A. Montgomery, K. Raghava-
chari, M. A. Al-Laham, V. G. Zakrzewski, J. V. Ortiz, J. B.
Foresman, J. Cioslowski, B. B. Stefanov, A. Nanayakkara, M.
Challacombe, C. Y. Peng, P. Y. Ayala, W. Chen, M. W. Wong,
J. L. Andres, E. S. Replogle, R. Gomberts, R. L. Martin, D. J. Fox,
J. S. Binkley, D. J. Defrees, J. Baker, J. P. Stewart, M. Head-
Gordon, C. Gonzales and J. A. Pople, Gaussian, Inc., Pittsburgh
PA, 1995.
0
=
c
each temperature by non-linear least-square Ðtting of this k
loss
expression to the calculated values obtained from our
““combined mechanism.ÏÏ The calculated value of F , accord-
ing to the Troe procedure, is ca. 0.55È0.6 at 298 K, corre-
c
sponding to C B 600. However, as the best Ðt obtained at
each temperature leads to C B 900, (F B 0.7 at 298 K), this
c
latter value is retained. The following optimized expressions
are then derived: k (T ) \ 2.65 ] 10~29 (T /298 K)~2.8
0
cm6 molecule~2 s~1;
k \ 3.26 ] 10~11 (T /298 K)~0.6
=
cm3 molecule~1 s~1; Cst \ 1.25 ] 10~11 exp ([1015
K/T ) ] 1.92 ] 10~12 (T /298 K)~2.56 cm3 molecule~1 s~1;
F \ exp ([T /900 K), for He as bu†er gas.
c
Conclusion
By a multichannel RRKM analysis of the pressure and tem-
perature dependence of the rate constant for the reaction
CH O ] NO, it is established that the disproportionation
3
reaction to CH O ] HNO products may occur simulta-
2
neously (i) by a direct hydrogen abstraction reaction and (ii)
via the formation of energized CH ONO* complex in com-
3
petition with the association reaction. This analysis is con-
30 J. A. Pople, H. B. Schlegel, R. Krishnan, D. J. De Frees, J. S.
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31 A. D. J. Becke, J. Chem. Phys., 1993, 98, 5648; C. Lee, W. Yang
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32 T. H. Dunning Jr., J. Chem. Phys., 1989, 98, 1007.
33 D. L. Osborn, D. J. Leahy, E. M. Ross and D. M. Neumark,
Chem. Phys. L ett., 1995, 235, 484.
Ðrmed by the result of ab initio calculation of the PES of this
system. The proposed kinetic modelling, accounts for the
major part of the available experimental results. It allows a
reliable representation of the overall rate constant and pre-
dicts the evolution of the branching ratios, for the 1È760 Torr
and 220È600 K pressure and temperature ranges.
34 L. A. Curtiss and L. D. Koch, J. Chem. Phys., 1991, 95, 4040.
35 S. Dertinger, A. Geers, J. Kappert, J. Wiebrecht and F. Temps,
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Acknowledgements
We thank the Centre dÏEtudes et Recherches Lasers et Appli-
cations (CERLA) supported by Ministere charge de la
Recherche, Region Nord/Pas de Calais et Fonds Europeen de
Developpement Economique des Regions (FEDER) for Ðnan-
cial support. M.T.R. is grateful to C. F. Melius, who kindly
provided his BAC-MP4 program package.
36 R. Silverwood and J. H. Thomas, T rans. Faraday Soc., 1967, 63,
2476.
37 D. R. Stull, E. F. Jr. Westrum and G. C. Sinke, T he Chemical
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38 W. Forst, Programm FALLOFF, QCMP, 121, QCPE, 1993, 13,
21.
39 W. Forst, J. Phys. Chem., 1991, 95, 3612.
40 W. Forst and F. Caralp, J. Chem. Soc., Faraday T rans., 1991, 87,
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