Chemical, electron, and desorption ionization and photoionization, together with photodissociation and high- and low-energy collisional activation, are used to probe the unusual mass spectrometric behavior of polycyclic aromatic hydrocarbons. The extent of fragmentation and even the types of dissociation products are dependent on the activation method used. This is rationalized in terms of energy deposition functions. The method used to deposit energy may also have effects in some cases. Doubly charged and protonated molecules are included in the comparisons made here. Furthermore, parent ions having different masses and structures produce common sets of low-mass fragment ions. The similarity in the spectra of different parent ions results from an unusual proclivity for rearrangement after excitation. Extensive rearrangement is favored because the ions studied have high internal energy capacity as indicated by the abnormally large energies required for dissociation. Thus, irreversible ring opening may take place, followed by eliminations of small neutral molecules to form intermediate ions common to many PAH molecules. These ions are suggested to have structures with unbranched cumulated double bonds. Their further fragmentation yields sets of low-mass fragment ions which are common for all parent ions derived from different PAH molecules.
ASJC Scopus subject areas
- Colloid and Surface Chemistry