Production of PAH cations with narrow internal energy distribution using single nanosecond pulsed laser
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THE EUROPEAN PHYSICAL JOURNAL D
Regular Article
Production of PAH cations with narrow internal energy distribution using single nanosecond pulsed laser M.V. Vinitha1,a , Arya M. Nair2 , and Umesh R. Kadhane1 1 2
Indian Institute of Space Science and Technology, Thiruvananthapuram 695547, Kerala, India Government College, Karyavattom, University of Kerala, Thiruvananthapuram 695581, Kerala, India Received 16 June 2020 / Received in final form 28 July 2020 / Accepted 9 September 2020 Published online 1 November 2020 c EDP Sciences / Societ`
a Italiana di Fisica / Springer-Verlag GmbH Germany, part of Springer Nature, 2020 Abstract. The internal energy dynamics of three examples of PAHs are probed using a high resolution energy time of flight spectrometer. The measured H-loss rates are converted to internal energy values for a range of UV photon wavelengths. Multi step multi photon absorption scheme is proposed to estimate the possible internal energy values with reasonable accuracies. This was possible because of the ultrafast radiationless internal conversion process in PAHs and their structural rigidity. Thus, a method is proposed to produce PAH cations with narrow and known internal energy distribution using a single nanosecond pulsed laser, paving a way to study statistical unimolecular decay in PAHs very efficiently.
1 Introduction Unimolecular dissociation processes are often used as an interesting tool to understand the quantum behaviour of molecules. The non-statistical dissociations are usually specific to the topography of potential energy surface of excited electronic state of a given target molecule [1]. But the statistical dissociations are more generic in nature and can be identical for a given family of molecules [2]. The statistical dissociations are often critical for biomolecules and several other organic molecules, particularly for polycyclic aromatic hydrocarbons (PAHs) while interacting with energetic radiations [2,3]. The statistical dissociation of PAHs has become a central topic for many investigations. It is because of the generic nature of molecular dynamics of PAHs and their importance in astronomical and terrestrial environments [4–6]. This curiosity is further enhanced by the fact that these molecules under specific situations may breed biologically important molecules in interstellar medium [7]. Any systematic measurement of statistical dissociation of a molecule demands a good control of internal energy. This can be achieved by either cooling the molecules to very low temperature in ion traps followed by excitation by known energy or knowing the initial energy as accurately as possible [8,9]. In some rare cases explicit measurement of internal energy distribution is carried out [9,10]. This information is then used in modelling the decay curve of molecules [11]. The techniques like photoelectron photoion coincidence spectroscopy (PEPICO), iPEPICO and tPEPICO etc. are often used in conjunction a
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with the synchrotron radiation sources in order to identi
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