PAH radiative cooling and fragmentation kinematics studied within an electrostatic ring

R Brédy,S Martin,A R Allouche,C Joblin,L Chen,C Ortéga,J Bernard,M Ji,A Cassimi

doi:10.1088/1742-6596/583/1/012042

Abstract

Radiative cooling of polycyclic aromatic hydrocarbon (PAH) cations has been studied using a compact electrostatic ion storage ring, the Mini-Ring, in a time range up to 8 ms. The time evolution of the internal energy distribution of the ensemble of stored ions shows evidences of fast cooling which is attributed to the fluorescence from thermally excited electronic states. The internal energy distribution was probed by inducing unimolecular dissociation with single-photon absorption at given storage times. Information on the fragmentation kinematics and the dissociation channels were obtained by analyzing the image of the emitted neutrals detected with a time and position sensitive detector.

Highlights

Interests for polycyclic aromatic hydrocarbons (PAH) have been developed since almost thirty years as these molecules are considered as good candidates to explain the unidentified infrared emission bands observed in some interstellar regions [1]
It is well known that the main dissociation channels of PAH are the loss of hydrogen (H, H2) and acetylene (C2H2) depending on the size and internal energy of the molecule [8,9,10]
In this paper we report on the measurement of the population decay of anthracene cations at a given internal energy by analyzing the shift of the internal energy distribution (IED) as a function of time

Summary

Introduction

Interests for polycyclic aromatic hydrocarbons (PAH) have been developed since almost thirty years as these molecules are considered as good candidates to explain the unidentified infrared emission bands observed in some interstellar regions [1]. Evidences of fast radiative cooling have been observed very recently for anion clusters [12, 13] and anthracene cations [14] using ion storage techniques This fast cooling was attributed to fluorescence emission from low lying electronic excited states predicted by Leger et al [7, 11]. In this paper we report on the measurement of the population decay of anthracene cations at a given internal energy by analyzing the shift of the IED as a function of time This population decay is directly related to the radiative cooling mechanism and could be compared with the calculated fluorescence emission rate due to the electronic transition. The IED of the ensemble of the stored ions was probed using laser induced dissociation and preliminary results on the fragmentation kinematics of other PAH cations (naphthalene, pyrene) are presented

Radiative cooling of anthracene cations

Fragmentation kinematics

Findings

Conclusion