Differential electron emission from polycyclic aromatic hydrocarbon molecules under fast ion impact

Shubhadeep Biswas,Lokesh C Tribedi,P F Weck,Christophe Champion

doi:10.1038/s41598-017-05149-8

Abstract

Interaction between polycyclic aromatic hydrocarbon (PAH) molecule and energetic ion is a subject of interest in different areas of modern physics. Here, we present measurements of energy and angular distributions of absolute double differential electron emission cross section for coronene (C24H12) and fluorene (C13H10) molecules under fast bare oxygen ion impact. For coronene, the angular distributions of the low energy electrons are quite different from that of simpler targets like Ne or CH4, which is not the case for fluorene. The behaviour of the higher electron energy distributions for both the targets are similar to that for simple targets. In case of coronene, a clear signature of plasmon resonance is observed in the analysis of forward-backward angular asymmetry of low energy electron emission. For fluorene, such signature is not identified probably due to lower oscillator strength of plasmon compared to the coronene. The theoretical calculation based on the first-order Born approximation with correct boundary conditions (CB1), in general, reproduced the experimental observations qualitatively, for both the molecules, except in the low energy region for coronene, which again indicates the role of collective excitation. Single differential and total cross sections are also deduced. An overall comparative study is presented.

Highlights

Understanding of few-body collision dynamics has been a subject of intense research in past few decades
It is instructive to study the interaction of MeV energy ions with polycyclic aromatic hydrocarbon (PAH) molecules as it can provide information about how the PAHs are processed by the low-energy cosmic ray in the interstellar medium (ISM), and it helps to provide crucial inputs to various astrophysical models[13]
The clearer visibility of the peak in the backward angles compared to the forward and the intermediate angles is due to the fact that the cross section corresponding to the Coulomb ionization continuum is less at backward angles compared to the other angle, whereas the K-LL Auger cross section distribution is almost isotropic in nature

Summary

Introduction

Understanding of few-body collision dynamics has been a subject of intense research in past few decades. The question of heating and cooling of the IS gases automatically came into picture since the first determination of temperature of the ISM by 21 cm emission/ absorption line measurements In this respect, C allotropes play an important role because these are the main suppliers of free electrons in the IS clouds, contributing to the heating of ISM11. In the IS environment, cosmic ray (CR) is an important component It consists of protons, α-particles, heavier ions and electrons of energies spanning from few eV to hundreds of GeV. Unlike C6019–23 or metals[24] or large nucleus[25], PAHs are not well explored in the context of collective plasmon resonance In this respect the study of electron emission from these molecules can enlighten the issue suitably, as electron emission channel is the fastest mode of de-excitation of these resonances[24]. The question remains whether such plasmon excitation is realizable in other PAH molecules or not

Methods

Results

Conclusion