Inficon Transpector CPM User Manual

5–17
Transpector CPM Operating Manual
5.3.1.3 Electron Energy Effects
The exact fragmentation pattern will depend on the energy of the bombarding
electrons. Figure 5-8 graphs the number of argon ions (of different charge states)
produced per incident electron per Torr of gas pressure as a function of electron
energy.
Figure 5-8 Electron energy effects
This graph shows the number or argon ions, N, formed per electron per Torr at
0°C versus electron energy.
The appearance potential—the minimum electron energy required to produce a
specific ion—for Ar
+
is 15.7 eV. The number of argon ions produced rises steeply
with energy until a maximum is reached at about 55 eV. As the electron energy
rises above this level, the rate of Ar
+
production slowly decreases.
Typically in mass spectrometry, electron impact ionization is carried out at an
electron energy of 70 eV for two reasons:
 70 eV is above the minimum energy required to produce at least some positive
ions from any sufficiently volatile chemical species.
 70 eV is near the energy at which the rate of ion production is at its maximum
for most of the common gases.
Operating at 70 eV provides a universal detector with good sensitivity for gases
typically encountered.
12
10
8
6
4
2
0
N
100
200
300
400
500
Electron Energy (eV)
Ar
+
Ar
3+
x10
Ar
4+
x100
Ar
2+
From a paper by W. Bleakney, Physical Review, 36, p. 1303, published in 1930.

Inficon Transpector CPM Specifications

General

Brand	Inficon
Model	Transpector CPM
Category	Industrial Equipment
Language	English