[ajax0604]

I've read that a bonding or non-bonding electron could be knocked off due to electron bombardment in a mass spectrometer. If a non-bonding electron was knocked off, a molecular/parent ion would be formed (which could fragment down the track) but if a bonding electron was knocked off, would that fragment the molecule straight away and not produce a parent ion?

[marquis]

I don't know the answer, but can tell you where to look.

Try "Interpretation of Mass Spectra" by Fred McLafferty and Frantisek Turecek.

Hopefully, that will give you the answer.

Good luck.

[voidSetup]

It depends on the structure of the molecule.  Aromatics and conjugated pi-electron systems tend to show a more stable molecular ion so the abundance would be greater.  You can still see a molecular ion for a regular branched alkane, however the radical cation character of the molecular ion is delocalized over all of the covalent bonds in the molecule.  Depending on how quickly it fragments from there, you may not see a molecular ion or the abundance may be low.