ChemAtom Seminar: Najeeb Punnakayathil (SU Atom)

Title: Plasmon excitation and subsequent isomerization dynamics in PAHs under fast proton interaction


Polycyclic aromatic hydrocarbons [PAHs] and their cations are well known terrestrial and interstellar compounds. The molecular processes of excitation, relaxation as well as fragmentation of PAHs are of great importance for understanding the formation, presence and chemistry under interstellar conditions. A prominent mode of excitation that has been experimentally identified in these classes of molecules is “giant plasmon resonance”, which is usually followed by autoionization.

In this talk, I will present our recent investigation on the interaction of two simplest PAHs, naphthalene and azulene with fast proton (velocity between 1.41 and 2.4 a.u) as a model of ion-PAH interaction system. Production of various intact and fragment ions in coincidence with electron emission, electron transfer to projectile or both are analyzed. The two targets being isomers, the rather obvious similarity in the fundamental ion-molecule collision energetics is quantitatively verified. Internal dynamics of these isomeric ions are compared by their neutral evaporation channels, wherein single plasmon excitation in conjunction with isomerization dynamics will be discussed. Evidence from dication evaporation energetics is used to invoke the double plasmon excitation model. A model based on the multi plasmon resonance explains the observed proton velocity dependence of double to single ionization cross sections.