Geoscience Reference
In-Depth Information
the polarization capture demonstrated an increase in the values of the rate constants
for the colliding pairs He(2
3
S)
He(2
1
S) and He(2
1
S)
He(2
1
S) comparable with
He(2
3
S)
He(2
3
S), which was confirmed in the experiment (see Table
1.1
). It
follows that the measured and calculated value of the rate constants of reactions
(
1.45
,
1.46
,
1.47
,
1.48
) should depend significantly on the relative populations of
the metastable states in the entrance channel of reaction.
The main component in the decaying plasma is the triplet metastable He(2
3
S)
atoms as a result of an effective quenching of the singlet metastable He(2
1
S) atoms
by an electron impact at the time of the order of 10
4
s. The singlet metastable states
play the main role in the active phase of the discharge and the early afterglow of
plasma. The He
2C
ions are formed here in the upper vibrational states. The time of
the arrival at the ion collector in the beam experiments is of the order of 5
10
6
s;
therefore, the vibrationally excited molecular ions with shorter lifetimes should not
register.
In addition, destruction channels of the upper vibrationally excited states of the
molecular ions leading to their dissociation in plasma usually occur. Therefore,
we should expect a decrease of the value ” obtained by the mass spectrometric
diagnostics of the helium plasma if the helium pressure increases. It is possible
that this is connected with one of the reasons for the difference of the value ” with
the results obtained in plasma experiments. The ionization constants measured in
the decaying plasma by plasma electron spectroscopy for binary metastable atom
collisions of helium, neon, argon, krypton, and xenon atoms at
T
D
300 K are 1.0-
1.5
10
9
cm
3
s
1
(Kolokolov and Kudryavtsev
1989
).
Constants measured for reactions involving two atoms Ne(
3
P
2
) are three times
smaller. According to the same data, the values ” lie in the range 0.05-0.10, close to
similar values for helium and the value of ” for the asymmetrical Ar
C
Kr process.
In the latter case, the constant value is 3.1
˙
0.6
10
9
cm
3
s
1
(Kolokolov and
Kudryavtsev
1989
).
As a result, we distinguish the following two important implications for low-
temperature plasma physics. First, the ionization rate constant for the pair collisions
of metastable atoms of the inert gases at room temperature, where the dominant
channel is the formation of the atomic ions, is of the order of 10
9
cm
3
s
1
.
Second, at the energy
E
< 0.1 eV, the coefficient ” increases with decrease in energy.
Consequently, the relative yield of the molecular ions in the cryogenic plasma is
markedly increased.
1.5.1.2
Interactions Between Metastable and Normal Atoms
(Asymmetrical Collisions)
Investigations of chemo-ionization in thermal PI collisions with He(2
3
S) and H(1
2
S)
(or deuterium) atoms
He
2
3
S
C
H
1
2
S
!
He
C
H
C
C
e
(1.49)
