Fragmentation patterns and daughter ions:
The molecular ion is not the just only ion detected in a mass spectrum. The molecular ion is a high-energy species that fragments to provide daughter ions which are as well detected in the spectrum. At first view, fragmentation might seem to be a random process, but fragmentation patterns are frequently characteristic of specific functional groups and demonstrate the existence of those groups.
Because of fragmentation, a mass spectrum consists of a large number of peaks of varying intensities. The most intense of these peaks is termed as the base peak and is generally because of a comparatively stable fragmentation ion rather than the molecular ion. Examples of stable ions are the tertiary carbonium (R3C+), oxonium (R2O+), allylic (=C-CR2+), benzylic (Ar-CR2+), aromatic (Ar+), and immonium (R3N+) ions.