Chemistry Reference
In-Depth Information
TABLE 3.5
Examples of Metastable Excited States of Rare Gas Atoms
and Molecules
Atom/Molecule
Atomic/Molecular State
Internal Energy [eV]
Lifetime [s]
He
1
S
20.6
2
·
10
−
2
[13]
He
3
S
19.82
6
·
10
−
5
Ne
3
P
0
16.7
3
P
2
Ne
16.62
3
P
0
Ar
11.72
44.9
3
P
2
Ar
11.55
55.9
A
3
u
N
2
6.17
2
a
1
O
2
0.98
TABLE 3.6
Ionization Energy and Electron Affinity of Selected Atoms
and Molecules
Ionization Energy
Electron Affinity
Atom/Molecule
ε
ion
[eV]
Atom/Molecule
ε
aff
[eV]
He
24.59
H
0.754
Ar
15.76
C
1.263
H
13.60
O
1.461
H
2
15.43
F
3.401
N
14.53
F
2
3.080
N
2
15.58
Cl
3.610
O
13.61
Cl
2
2.380
O
2
12.07
CH
1.238
CH
2
10.39
CH
2
0.652
CF
2
11.44
CF
2
0.165
Source:
Lide, D.R., ed.,
CRC Handbook of Chemistry and Physics,
CRC Press,
Boca Raton, FL, 2001.
Besides the ionization of neutral gas atoms and molecules or the formation of negative
ions, the inelastic electron-molecule collisions also represent an important channel
for production of
chemical reactive species
due to excitation of particles and/or
dissociation of molecules in atomic and molecular radicals, e.g.,
O
∗
e
−
+
O
2
→
+
O
+
e
−
,
ε
thres
∼
16 eV,
e
−
+
CF
4
→
CF
3
+
F
+
e
−
,
ε
thres
∼
12.5eV,
CF
3
e
−
+
CF
4
→
+
F
+
2
e
−
, ε
thres
∼
15.5 eV.
The produced atomic and molecular radicals may initiate manifold plasma chemical
reactions in further collision processes in the plasma volume or at plasma boundaries.
