chemical physics of discharges - Argonne National Laboratory

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Freezing. 3jpotnesise thzf eqxi1ii.ri.m is followed du.ri!ig the initial stages
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cf coccling withir, the quench t.&e. For he~xistic pill'poses,, assaw that equilib-
I ,.i.... - k.. IS cbeyed dwing te:nperat:ce decay tc\ epprosicately 3300 K, or more specifi-
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-,. -G~L;, tc that temperat-re vh5r-e ?qKilibri,x:i predicts the maximum number of moles
cf FCII tc be famed.
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Then assux tiiat eli reactions involving nitrogen species
, are froze:: at that point, sc chat even as ccoling continues negligible decomposi-
1 tio!? I;f the occurs.
i Chemical Reaction Kicetics. In :w,kiiig this series of seemingly unwarranted
ass.mptions, sone specific reacCiori retes have been implied to be very fast, while
, .otiisrs, very slow. Focuskg C.!I nitrzgen-containing species, the fcllowing types
cf reactio:. nave been ass;;risd tc be rapid iinaer the conditions developed in the '
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Q',ik:.x:iLng tube:
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Y
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14' + e- M
Further, the following have been assumed to be very slow:
HCD; - many steps - €I! + N2 + C (5)
To date a full description of the reaction kinetics of the H-C-N system, even
at moderate temperatures, is unavailable. In the recent shock tube study of
hhrshall, Jeffers, and Bauer29, preliminary results indicate that the equilibrium
in Reaction 4 may be achieved rapidly at elevated temperatures. However, the
evidence points to a rather complex reactior. mechanism for the thermal dissociation
of HCN, wherein many more steps are involved than mentioned here. The cornplexity
of this system was encodntererl in the earlier study of Robertson and
Pease3', and iil similar systems explored by Goy, Shaw and Pritchard3l.
Rapid dissociation/recombination rates have been determined for nitrogen,
ReactiOn 3, by Wray3*. Reactisn rate data is not available for Reacclon 2, nor
for otker reactions likely to be quite important in the H-C-8 system.
Atomic-ion/electror. recoxbination reactions for each of the three atoms in
the plasma are likely to be rapid33 relative to the quenching time.
In surnniary, existing reaction rate data is fa- from sicfficient to check the
assu-,pticns made abcut the reaction niectanisms apprcpriate to this H-C-N system.
kdiiti onal kinetic studies which generate presently unl.own reaction rates are
needed before an accurate reaction path cari be predicted theoretically for the
reacting H-C-N system.
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