Understanding the C3H2 cyclic-to-linear ratio in L1544

Abstract

Aims. We aim to understand the high cyclic-to-linear C3H2 ratio (32 ± 4) that has been observed toward L1544. Methods. We combined a gas-grain chemical model with a physical model for L1544 to simulate the column densities of cyclic and linear C3H2 observed toward L1544. The most important reactions for the formation and destruction of both forms of C3H2 were identified, and their relative rate coefficients were varied to find the best match to the observations. Results. We find that the ratio of the rate coefficients of C3H3+ + e- C3H2 + H for cyclic and linear C3H2 must be ~ 20 to reproduce the observations, depending on the branching ratios assumed for the C3H3+ + e- C3H + H2 reaction. In current astrochemical networks it is assumed that cyclic and linear C3H2 are formed in a 1:1 ratio in the aforementioned reactions. Laboratory studies and/or theoretical calculations are needed to confirm the results of our chemical modeling, which is based on observational constraints.