We report the detection of linear and cyclic isomers of C3H and C3H2 towards various starless cores and review the corresponding chemical pathways involving neutral (C3Hx with x=1,2) and ionic (C3Hx+ with x = 1,2,3) isomers. We highlight the role of the branching ratio of electronic Dissociative Recombination (DR) reactions of C3H2+ and C3H3+ isomers showing that the statistical treatment of the relaxation of C3H* and C3H2* produced in these DR reactions may explain the relative c,l-C3H and c,l-C3H2 abundances. We have also introduced in the model the third isomer of C3H2 (HCCCH). The observed cyclic-to-linear C3H2 ratio vary from 110 + or - 30 for molecular clouds with a total density around 1e4 molecules.cm-3 to 30 + or - 10 for molecular clouds with a total density around 4e5 molecules.cm-3, a trend well reproduced with our updated model. The higher ratio for low molecular cloud densities is mainly determined by the importance of the H + l-C3H2 -> H + c-C3H2 and H + t-C3H2 -> H + c-C3H2 isomerization reactions.
@article{arxiv.1707.07926,
title = {The interstellar chemistry of C3H and C3H2 isomers},
author = {Jean-Christophe Loison and Marcelino Agundez and Valentine Wakelam and Evelyne Roueff and Pierre Gratier and Nuuria Marcelino and Dianailys Nunnez Reyes and Josee Cernicharo and Maryvonne Gerin},
journal= {arXiv preprint arXiv:1707.07926},
year = {2017}
}