The characteristic spread of ion peaks a molecule produces when electron impact in the ion source breaks it apart, with relative heights fixed for given source settings. Water appears at 18 with fragments at 17 and 16, nitrogen at 28 with a fragment at 14, carbon dioxide at 44 with fragments at 28 and 16. Reading an RGA scan means subtracting known patterns peak by peak, which is how you tell nitrogen from carbon monoxide at mass 28.
Heard on the job
Big peak at 28 but almost nothing at 14, check the cracking pattern, it's CO, not nitrogen, so it's not air.
Also heard as
- fragmentation pattern
- fragment pattern