Inficon Transpector MPH - Ionization Process

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Transpector MPH Operating Manual
Figure 4-1 Example mass spectrum
4.1.1.1 Ionization Process
When a sufficiently energetic electron strikes a gas molecule, there are many
processes that can occur, just some of which are summarized in Table 4-1.
The bottom graph is a trend analysis showing the most important
masses versus time. The top graph shows the data taken during the
scan and shows the air spectra over a six decade y-axis. The
prominent peaks for air are mass 28 from Nitrogen, mass 32 from
Oxygen, mass 40 from Argon and mass 18 from water vapor.
Table 4-1 Electron impact ionization processes
XYZ
+
+ e
-

XYZ
+
+ 2e
-
(1)
XYZ
2+
+ 3e
-
(2)
XY + Z
+
+ 2e
-
(3)
XY
+
+ Z + 2e
-
(4)
X
+
+ YZ + 2e
-
(5)
X + YZ
+
+ 2e
-
(6)
XZ + Y
+
+ 2e
-
(7)
XZ
+
+ Y + 2e
-
(8)