Environmental Engineering Reference
In-Depth Information
and
k
0
are numerical coefficients, and if the atom excitation energy
is expressed
in electronvolts and the radiative lifetime is given in nanoseconds, the numerical
coefficient is [8]
k
0
Δ
ε
10
5
cm
3
/s,ifweusethedatafortheexcitation
cross sections of alkali metal atoms. As follows from the data in Table 2.7, the
accuracy of (2.58) for the quenching rate constants of resonantly excited states is
about 20%, and Table 2.8 contains the quenching rate constants of some resonantly
excited atoms quenched by electron impact. The rate constant for quenching of
atom metastable states by electron impact is lower than that for resonantly excited
states because of a weaker coupling between these states during interaction with
an electron. This is demonstrated by comparison of the data in Table 2.8 with those
in Table 2.9, where these rate constants are given for metastable inert gas atoms.
D
(4.4
˙
0.7)
Ta b l e 2 . 8
Parameters of resonantly excited atomic states of some atoms and the rate constant
for quenching of these states by slow electron impact.
k
q
,10
8
cm
3
/s
Atom, transition
Δ
ε
,eV
λ
,nm
f
τ
0
,ns
H(2
1
P
1
1
S
)
!
10.20
121.6
0.416
1.60
0.79
He(2
1
P
1
1
S
)
!
21.22
58.43
0.276
0.555
0.18
He(2
1
P
2
1
S
)
!
0.602
2058
0.376
500
51
He(2
3
P
2
3
S
)
!
1.144
1083
0.539
98
27
Li(2
2
P
2
2
S
)
!
1.848
670.8
0.74
27
19
Na(3
2
P
3
2
S
)
!
2.104
589
0.955
16.3
20
K(4
2
P
1/2
!
4
2
S
1/2
)
1.610
766.9
0.35
26
31
K(4
2
P
3/2
!
4
2
S
1/2
)
1.616
766.5
0.70
25
32
Rb(5
2
P
1/2
!
5
2
S
1/2
)
1.560
794.8
0.32
28
32
Rb(5
2
P
3/2
!
5
2
S
1/2
)
1.589
780.0
0.67
26
33
Cs(6
2
P
1/2
!
6
2
S
1/2
)
1.386
894.4
0.39
30
46
Cs(6
2
P
3/2
!
6
2
S
1/2
)
1.455
852.1
0.81
27
43
Ta b l e 2 . 9
The rate constant for quenching of metastable states of rare gas atoms by slow elec-
tron impact. The data are taken from [93].
Δ
ε
,eV
k
q
,10
10
cm
3
/s
Atom, transition
He(2
3
S
1
1
S
)
!
19.82
31
Ne(2
3
P
2
!
2
1
S
)
16.62
2.0
Ar(3
3
P
2
!
3
2
S
)
11.55
4.0
Kr(4
3
P
2
!
4
2
S
0
)
9.915
3.4
Xe(5
2
P
2
!
5
2
S
0
)
8.315
19
