Dissociative electron attachment to the unstable carbon ...

Dissociative electron attachment to CS 7
Counts
18000
16000
14000
12000
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2000
0
(a)
CS +
CS 2
+
10 12 14 16 18 20
Electron Energy (eV)
Counts
25000
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15000
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0
(b)
CS +
CS 2
+
10 12 14 16 18 20
Electron Energy (eV)
Figure 7. Intensities of CS + and CS + 2 observed with (a) the plasma off and (b) the
plasma on as a function of electron energy. The presence of CS in the gas sample with
the plasma on is confirmed by the appearance of CS + at the ionization energy of CS.
Counts
600
500
400
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100
0
(a)
C 2 S +
C 3 S 2
+
10 12 14 16 18 20
Electron Energy (eV)
Counts
400
350
300
250
200
150
100
50
0
(b)
S 2 O +
SO +
10 12 14 16 18 20
Electron Energy (eV)
Figure 8. (a) Intensities of C 2 S + and C 3 S + 2 as a function of electron energy with the
plasma on at high CS 2 inlet pressure and (b) intensities of SO + and S 2 O + with the
plasma on with low CS 2 inlet pressure.
energy of CS + from CS 2 .
CS is known to undergo spontaneous polymerisation reactions leading to species of
the type C n S m . Proposed reactions leading to the formation of C 3 S 2 are [26]
2CS → C 2 S + S (2)
C 2 S + CS → C 3 S 2 (3)
C 3 S + 2 and also weakly C 2 S + were observed in the positive ion mass spectrum with the
plasma on. Most of the C 2 S + detected, however, is likely to be due to dissociation of a
larger ion rather than ionization of C 2 S as the observed appearance energy is relatively
high at 15.5 ± 0.5 eV, see Figure 8(a). The ionization threshold of C 3 S 2 is determined
to be 9.4 ± 0.3 eV from the data shown in Figure 8(a). This is in good agreement
with a predicted vertical ionization energy of 9.19 eV calculated here with a GAMESS