# LES HYDROCARBURES DANS LE MILIEU INTERSTELLAIRE : DES NUAGES SOMBRES AUX REGIONS DE PHOTODISSOCIATION

Abstract : Hydrocarbons form the frame of the interstellar gas-phase chemistry. Yet, the distribution and the abundance of these species are known in a few objects only. After a short introduction to (\it astrochemistry), we deal with hydrocarbons in dark clouds in the second part of this PhD dissertation. We first show -- at the end of a work dedicated to the cloud TMC-1 -- that the abundance ratio of the cyclic and linear isomers of C$_3$H$_2$ depends on the electronic fraction in the gas and could therefore be used as a probe of this quantity. We also emphasize that C$_6$H and \lCCCHH, rarely observed until now, are common in dark clouds. Finally, we show that hydrocarbons are present in the envelope of the cloud L\,134N and that their abundances fit in with a carbon-rich chemistry. The third part is dedicated to observations of hydrocarbons in three photodissociation regions, including the Horsehead nebula. The maps we made show that hydrocarbons are present and abundant in zones illuminated by the ultraviolet field. Besides, their emission is spatially correlated with the PAH's. We notice that gas-phase chemistry models fail to reproduce these properties and emphasize that the photoerosion of PAHs -- not yet taken into account -- seems to succeed in producing hydrocarbons fast enough to reconcile models and observations.
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https://tel.archives-ouvertes.fr/tel-00003543
Contributor : David Fossé <>
Submitted on : Friday, April 16, 2004 - 12:58:59 AM
Last modification on : Thursday, December 10, 2020 - 12:37:51 PM
Long-term archiving on: : Monday, September 20, 2010 - 12:00:05 PM

### Identifiers

• HAL Id : tel-00003543, version 2

### Citation

David Fossé. LES HYDROCARBURES DANS LE MILIEU INTERSTELLAIRE : DES NUAGES SOMBRES AUX REGIONS DE PHOTODISSOCIATION. Astrophysique [astro-ph]. Université Pierre et Marie Curie - Paris VI, 2003. Français. ⟨tel-00003543v2⟩

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