Multiple ionization, fragmentation and dehydrogenation of coronene in collisions with swift protons

Abstract

Coronene molecules have been bombarded with protons of energy ranging from 100 to 300 keV. The time of flight mass spectra have been recorded using a two stage Wiley McLaren type spectrometer. A significant enhancement in the yields of doubly and triply ionized recoil ions is observed compared to the singly ionized ones. The single, double and triple ionization cross sections are also calculated theoretically using the continuum distorted wave eikonal initial state (CDW EIS) and are compared with the experimental results. The experimental ratios of yields of double to single charged and triple to single charged recoil ions are found to be much higher compared to those for the gaseous atoms. Evaporation peaks corresponding to the loss of several neutral C2H2 molecules are observed for singly, doubly and triply charged coronene recoil ions. Multi fragmentation peaks corresponding to smaller masses of carbohydrates CnHx (n = 3 to 7), appear in the spectra due to higher energy transfer from the projectile to the molecule. The yields of evaporation and fragment products exhibit a pronounced dependence on projectile energy, with a significant decrease observed at higher energies. Dehydrogenetaion i.e. loss of H atoms or H2 molecules are also investigated from the measured spectra. It is observed that hydrogen molecule losses are preferred over H loss in the cation and dication coronene peak structures, with up to three molecules being lost. This observation is in line with some of the predictions and may provide important inputs towards the astrochemistry regarding the observed abundance of H2 in the inter stellar medium.