Dissociation of the benzene molecule by ultraviolet and soft X-rays in circumstellar environment |
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Authors: | H M Boechat-Roberty R Neves S Pilling A F Lago G G B de Souza |
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Institution: | Observatório do Valongo, Universidade Federal do Rio de Janeiro - UFRJ, Ladeira Pedro Antnio 43, CEP 20080-090, Rio de Janeiro, RJ, Brazil;Pontificia Universidade Católica do Rio de Janeiro, Marqués de S. Vicente 255 CEP22543-970, Rio de Jeneiro, Brazil;Universidade Federal do ABC, Rua Santa Adélia, 166, Santo André, São Paulo, Brazil;Instituto de Química, Universidade Federal do Rio de Janeiro - UFRJ, Ilha do Fundão, CEP 21949-900, Rio de Janeiro, RJ, Brazil |
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Abstract: | Benzene molecules, present in the proto-planetary nebula CRL 618, are ionized and dissociated by ultraviolet (UV) and X-ray photons originated from the hot central star and by its fast wind. Ionic species and free radicals produced by these processes can lead to the formation of new organic molecules. The aim of this work is to study the photoionization and photodissociation processes of the benzene molecule, using synchrotron radiation and time-of-flight mass spectrometry. Mass spectra were recorded at different energies corresponding to the vacuum UV (21.21 eV) and soft X-ray (282–310 eV) spectral regions. The production of ions from the benzene dissociative photoionization is here quantified, indicating that C6H6 is more efficiently fragmented by soft X-ray than UV radiation, where 50 per cent of the ionized benzene molecules survive to UV dissociation while only about 4 per cent resist to X-rays. Partial ion yields of H+ and small hydrocarbons, such as C2H+2, C3H+3, C4H+2 , are determined as a function of photon energy. Absolute photoionization and dissociative photoionization cross-sections have also been determined. From these values, half-life of benzene molecule due to UV and X-ray photon fluxes in CRL 618 was obtained. |
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Keywords: | astrochemistry molecular data methods: laboratory ISM: molecules X-rays: stars |
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