Answer 2.5

a) Give rough estimates of the time needed for the following events:

electron ionization: low femtosecond time scale
bond vibration: low picosecond time scale
bond cleavage: pico- to nanoseconds
rearrangements: nano- to low microsecond time scale
residence time in ion source: about one microsecond
residence time in mass analyzer: tens of microseconds

b) What is the difference between stable, unstable and metastable ions in mass spectrometry?

Stable ions reach the detector without any fragmentation (k < 105 s–1).
Metastable ions decompose in transit (105 s–1 < k < 106 s–1) and unstable ions dissociate still within the ion source (k > 106 s–1).