Ions Colliding with Cold Polycyclic Aromatic Hydrocarbon Clusters

We report the first experimental study of ions interacting with clusters of polycyclic aromatic hydrocarbon (PAH) molecules. Collisions between 11.25 keV ³He⁺ or 360 keV ¹²⁹Xe²⁰⁺ and weakly bound clusters of one of the smallest PAH molecules, anthracene, show that C₁₄H₁₀ clusters have much higher tendencies to fragment in ion collisions than other weakly bound clusters. The ionization is dominated by peripheral collisions in which the clusters, very surprisingly, are more strongly heated by Xe²⁰⁺ collisions than by He⁺ collisions. The appearance size is $k=15$ for [C₁₄H₁₀]ₖ²⁺.