Chemistry Reference
In-Depth Information
0 0 0 0 0 0 0 0 0 0
0
8
8
7
7
e + O(
3
P)
6
6
5
5
4
4
O*(3p
3
P)
3
3
2
2
O * (3p
5
P)
1
1
0
0
0 0 0 0 0 0 0 0 0 0 0
Electron energy in eV
FIGURE 3.20
Electron excitation cross section of ground state atomic oxygen O(
3
P) into the
levels O(3p
3
P) and O(3p
5
P) in dependence on the electron energy according to the listed data
in [22]. (Data from Laher, R.R. and Gilmore, F.R., Updated excitation and ionization cross
section for electron and impact on atomic oxygen, Technical Report, R & D Associates Marina
Del Rey, CA, 1988.)
spectrum is influenced by many factors, e.g., the electron energy distribution function,
thedirectordissociativeexcitation,thecascadeprocesses,thebranching,theradiation
transport, and the collision of excited particle which may result in de-excitation
without radiation. All these factors have influence on the emission intensity, the
line broadening, or the ro-vibrational band structures of electronic transitions in
molecules. Generally, the quantum physics of the elementary excitation and de-
excitation processes and the collision-radiation model have to be involved to achieve
exactly the appropriate information from the measured emission spectrum for further
analysis.
Asanexample,theelectronimpactexcitationcrosssectionofatomicoxygenfrom
the ground state O(
3
P) into the levels O(3p
5
P) and O(3p
3
P) is shown in Figure 3.20
[22]. These states are the upper levels of the intensive optical transitions at 777 and
844 nm into the O(3s
5
S) and O(3s
3
S) state, respectively.
The optical emission cross section σ
opt
can be directly determined from measured
data in electron beam experiments according to (3.112) [20,23].
4π
e
n
gas
·
·
s
·
γ
s
(
λ
)
·
R
c
σ
opt
(
i
→
j
)
=
I
e
·
·
A
s
·
F
(
λ,
T
)
·
λ
(3.112)
L
·
c
·
γ
c
(
λ
)
·
R
s
with
I
e
the electron current,
L
path length of the electron beam, and
n
gas number
density.
The terms in the bracket describe the measured total photon flux per second
for the atomic transition
i
→
j
, with an effective radiation area of the standard
