Journal Article

Dissociation of the benzene molecule by ultraviolet and soft X-rays in circumstellar environment

H. M. Boechat-Roberty, R. Neves, S. Pilling, A. F. Lago and G. G. B. De Souza

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 394, issue 2, pages 810-817
Published in print April 2009 | ISSN: 0035-8711
Published online March 2009 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2008.14368.x
Dissociation of the benzene molecule by ultraviolet and soft X-rays in circumstellar environment

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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.

Keywords: astrochemistry; molecular data; methods: laboratory; ISM: molecules; X-rays: stars

Journal Article.  4603 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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