Madhusree Roy Chowdhury
Institute of Physics, University of Kassel, Germany
In the first part of my talk, I will discuss the VUV photoionization and fragmentation of the cyano-substituted PAHs, recently detected in the interstellar medium (ISM). Unlike most of the PAHs which are postulated to exist abundantly in the ISM through the observation of aromatic infrared emission bands (AIBs) but are not detected individually due to their highly symmetric molecular structures, the two isomers of cyanonaphthalenes (CNN) have been detected in the cold Taurus molecular cloud (TMC-1) [1], having a functionalized nitrile (or cyanide) group. Ionization of PAHs leads to gas heating by thermalization of emitted electrons [2,3]. These free PAHs are produced by evaporation of carbonaceous very small grains (C-VSGs) under VUV irradiation. To understand the impact of VUV light on C-VSGs, I will show recent results on photoemission spectra from nanoparticles of PAHs.
In the second part, I will focus on the radiation induced damage in DNA/RNA nucleobases. I will discuss the case of valence shell ionization of halouracils, a class of radiosensitizers used in radiation therapy. Emission of electrons is the primary step for damaging the DNA/RNA of the malignant cells. When the incident beam of photons or ions interact with the biomolecules, secondary electrons, ions, excited molecules are formed along with the production of hydroxyl radicals due to interaction with surrounding water molecules. In this context, radiosensitizers are targeted drugs that increases the lethal effects of radiation particularly on the tumor [4].
I will further discuss about core-level ionization of biomolecules embedded in an aqueous environment. Along with the local Auger decay, non-local decay channels like Intermolecular Coulombic decay (ICD) [5] and Electron Transfer Mediated Decay (ETMD) become dominant due to the presence of the environment, ionizing both the biomolecule and its neighbours.
The experiments for the above projects have been carried out at the DESIRS beamline of Synchrotron SOLEIL [6] and FinEstBeAMS beamline at MAX IV [7] using electron-ion coincidence spectroscopy.
1. B. A. McGuire et. al. Science 371, 1265 (2021)
2. O. Berné et. al. A&A 667, A159 (2022)
3. M. Roy Chowdhury et. al. ApJ 963, 29 (2024)
4. K. T. Butterworth et. al. Radiation Research 170, 381 (2008)
5. T. Jahnke et. al., Chem. Rev. 120, 11295 (2020)
6. G. A. Garcia et. al. Rev. Sci. Inst. 84, 053112 (2013)
7. K. Kooser et. al., J. Synchotron Rad., 27, 1080 (2020)