Chemistry Reference
In-Depth Information
with rate coefficient
k
ABC
depending on the square root of the gas temperature.
8
m
red
∼
√
T
.
·
k
B
T
k
ABC
=
σ
ABC
HS
·
v
r
=
σ
ABC
HS
·
(3.150)
π
·
3.5.3.2 Rate Coefficient for Ion-Molecule Reactions with the Langevin
Capture Cross Section
Considering the ion-molecule reaction
A
+
+
AB
+
BC
−→
+
C,
(3.151)
the reaction rate
dn
A
dt
dn
BC
dt
v
r
·
v
r
)
·
L
=
L
=−
σ
A
+
BC
L
(
n
A
+
·
n
BC
(3.152)
n
BC
τ
A
+
=−
k
A
+
BC
L
·
n
A
+
·
n
BC
=−
ν
A
+
·
n
BC
=−
can be calculated by use of the Langevin capture cross section
1
/
2
α
BC
·
q
A
1
v
r
σ
A
+
BC
L
(
v
r
)
=
∼
(3.153)
ε
0
·
m
red
·
v
r
and the Maxwellian velocity distribution with the same temperature for the neutral
gas and the ions
T
gas
=
T
. The corresponding rate coefficient
k
A
+
B
L
is calculated
for the particle capture, which may be an estimation for the rate coefficient for ion-
molecule reactions at low relative velocity in nonthermal plasmas. This capture rate
coefficient
k
A
+
BC
L
T
+
=
depends not on the temperature and particle velocity.
α
BC
m
red
·
α
BC
m
red
.
∞
=
σ
A
+
BC
L
v
r
=
q
A
ε
0
·
q
A
ε
0
·
k
A
+
BC
L
(
v
r
)
·
f
(
v
r
)
·
dv
r
=
(3.154)
0
3.5.3.3 Rate Coefficient for Neutral-Neutral Reactions with
Threshold Energy
The reaction
ε
CDE
thres
−→
C
+
DE
CD
+
E
(3.155)
and the corresponding reaction rate
dn
CD
dt
dt
=
v
r
·
v
r
)
·
dn
C
dt
=−
dn
DE
σ
CDE
thres
thres
=−
(
n
C
·
n
DE
n
DE
τ
C
=
k
CDE
thres
·
n
C
·
n
DE
=
ν
C
·
n
DE
=
(3.156)
