chemical physics of discharges - Argonne National Laboratory

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A number of investigators have subsequently studied this chemi-ionization reaction of\
the rare gas ions and have confirmed and extended Hornbeck and Molnar's observation,
It has now been observed that all of the rare gases react with each other to form
.the hetero-nuclear diatomic ions (57). In addition, a number of ionic compounds of ,
the rare gases with nitrogen, CO, 02, methane, acetylene and others have been report-'
ed. Chemi-ionization reactions are not necessarily limited to rare gases, however. , !
Chemi-ionization products of excited mercury atoms with a number of compounds have
been observed (59) and nitrogen and CO are known to und r o chemi-ionization with
their own ground state species, forming respectively N -? :nd C20; '(32).
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(59) P. Cermak and 2. Herman, Tenth Annual Conference on Mass Spectrometry, New
I
,
Orleans, La., 1962, p. 358. I
,
It is natural that when both reactants and products are readily measurable
c nsiderat'on should early be given to the fate of the reaction. With the reaction
4? + S, if M is much larger than A , the feactior rate is psuedo first order'
A + M -%
and the equation expressing the concentration of A and B is as follows:
- B+ =
AO
+
-kMt
1-e
-
-1
A Llot of B+ against M will yield a straight line whose slope is kt. If a
At relatively low pressures, (a few microns), i
time is thus:
B+
- =
A' + B+
rate constants for second order ion-molecule reactions are given in table 11. It
will be observed that many 2 them are in the order of 10 cc/molecule/sec. How-
€3
ever, values as small as 10 cc/mo_l culelsec have been reported for some reactions.
6 The values in the neighborhood of 10 cc/molecule/sec represent reactions that must
occur at essentially every collision in that they have cross sectionslSonsiderably
larger than ordinary collision cross sections. The values around 10 represent
or very small.
must not involve appreciable energy of activation. Stevenson and Schissler (4,11)
have confirmed this experimentally for a few reactions and the very fact that a
kMt
As was mentioned before, ion-molecule reactions to be observable ,
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