Multiple ionization and fragmentation of isolated pyrene and coronene molecules in collision with ions

Abstract

The interaction of multiply charged ions (He${}^{2+}$, ${\mathrm{O}}^{3+}$, and Xe${}^{20+}$) with gas-phase pericondensed polycyclic aromatic hydrocarbon (PAH) molecules of coronene (C${}_{24}$H${}_{12}$) and pyrene (C${}_{16}$H${}_{10}$) is studied for low-velocity collisions ($v\ensuremath{\leqslant}0.6$ a.u.). The mass spectrometric analysis shows that singly and up to quadruply charged intact molecules are important reaction products. The relative experimental yields are compared with the results of a simple classical over-the-barrier model. For higher molecular charge states, the experimental yields decrease much more strongly than the model predictions due to the instabilities of the multiply charged PAH molecules. Even-odd oscillations with the number of carbon atoms, $n$, in the intensity distributions of the ${\mathrm{C}}_{n}$H${}_{x}^{+}$ fragments indicate a linear chain structure of the fragments similar to those observed for ion-C${}_{60}$ collisions. The latter oscillations are known to be due to dissociation energy differences between even- and odd-$n$ ${\mathrm{C}}_{n}$-chain molecules. For PAH molecules, the average numbers of H atoms attached to the ${\mathrm{C}}_{n}$H${}_{x}$ chains are larger for even-$n$ reflecting acetylenic bond systems.