Geoscience Reference
In-Depth Information
Table 2.1.
Reaction rate
β
in
for the ion-induced molecular polarization[22]
10
10
cm
3
/
s
ion-neutral pairs
Q
=
β
in
×
Q
Q
Q
O
+
,
N
2
NO
+
,
N
2
H
+
,
N
2
5.1
9.0
2.4
O
+
,
O
2
NO
+
,
O7.6
+
,
He
4.5
4.3
O
+
,
He
NO
+
,
H21
e
+
,
O4.5
2.2
O
+
,
H
NO
+
,
He
He
+
,
H7.7
2.6
6.4
NO
+
,
O
2
H
+
,
O
2
He
+
,
N
2
8.3
2.7
4.1
Ion-Neutrals
The ion-induced dipole interaction dominates during collisions of ions and
neutral particles at moderate temperatures
T
500
o
K [19]. In this case,
the collision frequencies of different ions with molecules are independent on
temperature and given by [7]
∝
300
−
ν
in
=
β
in
N
n
,
where
N
n
is concentration of neutral particles per cm
3
. Coecients
β
in
are
given in Table 2.1 [22].
Intercharge processes dominate under collisions of ions and molecules of
the same kind,
X
+
+
X
X
+
X
+
. An effective collision frequency for this
process is found from the approximate expression
⇒
ν
in
=
β
in
(
T
i
+
T
n
)
1
/
2
N
n
.
β
in
for different kinds of recharges are shown in Table 2.2 ([7], [22]).
Assuming that ions and neutral gas have the Maxwell's distribution, the
effective ion-neutral collision frequency
ν
in
is given by [15]
10
−
9
(
N
n
+
N
i
)
M
−
1
/
2
.
ν
in
=2
.
6
×
(2.3)
N
i
is ion concentration. Ion mass
m
i
and molecular mass
m
n
are presumed
to be the same,
M
=
m
i
=
m
n
. The line '
i
−
m
' of Fig. 2.3 shows height
Table 2.2.
Reactionrate Coecients
β
in
for the charge interchange ([7], [22])
β
in
×
10
9
cm
3
/
s
×
eV
1
/
2
ion-molecule pairs
O
+
,
O
1.8
O
2
,
O
2
1.2
H
+
,
H
11
He
+
,
He
3.3
N
2
,
N
2
2.3
N
+
,
N
1.8
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