Chemistry Reference
In-Depth Information
1400
1200
1000
1
2
3
4
5
6
800
600
400
200
0
0.0
0.5
1.0
1.5
p
[mbar]
FIGURE 6.8
Translational and rotational temperatures in a planar microwave discharge
(64% H
2
+
16% D
2
+
20% Ar,
P
=
1.5 kW) and their dependence on pressure, 1, 2, and 3:
translational temperatures derived from Doppler broadening of D
α
,H
α
,andH
2
spectral lines
respectively; 4, 5, and 6: rotational temperatures of the X
1
0 state of H
2
obtained from
the
Q
(0-0),
Q
(1-1), and
Q
(2-2) branches of the Fulcher-α bands. (From Röpcke, J. et al.,
J.
Phys.IV
, 8, 207, 1998,
ThirdInternationalWorkshoponMicrowaveDischarges-Fundamentals
and Applications
, April 20-25, 1997, Fontevraud Abbey, France.)
g
, ν
=
applications in plasma technology) is the application of internal checks within the
method—to use simultaneously the emission of several different bands and band
systems [177,188], different isotopomers (like H
2
, HD, and D
2
[192]), or different
molecules [175,191] to determine
T
, which has obviously a specific value for every
condition.
As an example Figure 6.8 shows the results obtained in a planar microwave
discharge [175]. Agreement was found to be within 10%-15% between the
rotational temperature, derived from the (0-0), (1-1), (2-2) Fulcher-α bands, and the
translationaltemperaturesofhydrogenanddeuteriumatomsandhydrogenmolecules.
6.3.3.3.3 Vibrational Temperature
Population density distributions over vibrational levels have a non-Boltzmann char-
acter in gas discharge plasmas [200]. Nevertheless, the vibrational temperature
T
vib
is widely used for very rough estimates of these distributions. Since the original
measurement of the emission band intensities has been proposed for determining
T
vib
in N
2
discharges by OES [201], the method has often been used in low-pressure
plasma diagnostics. In particular, it looks promising for the in-situ control of tem-
perature during plasma processing. The method has been generalized by taking into
account the resolved rotational structure of H
2
bands [196], which is important for
