Formation and decay of doubly charged ions in n-alkanes from methane to triacontane

Coincidence techniques were used to study dissociative double ionization of selected n-alkanes from methane to triacontane (C₃₀H₆₂) and of the hexane isomers. Following photoionization at 40.8 eV, both covalent and coulombic dissociations of the molecular dications take place. The main decay route of doubly charged alkanes larger than butane is fast charge separation followed by secondary dissociation of energetic singly charged primary ions. A simulation based on quasi-equilibrium theory and the spectra of the isomers confirm this breakdown mechanism for hexane.