Dissociative electron attachment to the unstable carbon ...

Dissociative electron attachment to CS 6
Counts
18000
16000
14000
12000
10000
8000
6000
4000
2000
0
(a)
O 2 /S + CS + CS 2
+ C 3 S 2
+
C +
2000 4000 6000 8000
Time of flight (ns)
Counts
450
400 (b) CS +
350
300
O 2 /S +
+ SO + S 2 O +
250 N 2
200
OCS +
+ + + +
150 S 2 CS2
100 H 2 O +
S 5 S7
50
C +
0
2000 4000 6000 8000
S 3
+ S4
+ S6
+ S8
+
Time of flight (ns)
Figure 5. Positive ion mass spectra with the plasma on and different inlet pressures
of He and CS 2 ; the inlet pressure of CS 2 is high in (a) and low in (b). The electron
energy is ∼ 20 eV in both spectra.
Counts
12000
10000
8000
6000
4000 O 2 /S + CS +
CS 2
+
2000
+
H
S 2 2 O +
0
2000 4000 6000 8000
Time of flight (ns)
Figure 6. Positive ion mass spectra of He + CS 2 with the plasma off. The electron
energy is ∼ 20 eV, which is, of course, below the ionization energy of helium.
mass spectra recorded at ∼ 20 eV electron energy of the gas in the inlet system with (a)
a high inlet pressure of CS 2 and (b) a low pressure of CS 2 . At high CS 2 inlet pressure,
Figure 5 (a), the CS + signal is very strong whereas at low CS 2 pressure, Figure 5 (b),
S + n ions and background gas ions (H 2 O + , N + 2 , O + 2 ) are clearly visible. For comparison,
a mass spectrum of CS 2 and He with the plasma off is shown in Figure 6.
The presence of CS in the gas sample with the plasma on is confirmed by the
appearance energy measurement shown in Figure 7 for CS + . Values of 13.6-16.2 eV
have been reported for appearance energy for CS + from CS 2 whereas the evaluated
literature value of the ionization energy of CS is 11.3 eV [25]. The observed appearance
energy of CS + here with the plasma on, 11.3 ± 0.3 eV, is in good agreement with
ionization energy of CS. The appearance energy of CS + with the plasma off observed
here, 16.0 ± 0.5 eV, is not out of line with previous measurements for the appearance