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Aims. We aim to understand the high cyclic-to-linear $\rm C_3H_2$ ratio ($32\pm 4$) observed toward L1544 by Spezzano et al. (2016). Methods. We combine agas-grain chemical model with a physical model for L1544 to simulate the columndensities of cyclic and linear $\rm C_3H_2$ observed toward L1544. The mostimportant reactions for the formation and destruction of both forms of $\rmC_3H_2$ are identified, and their relative rate coefficients are varied to findthe best match to the observations. Results. We find that the ratio of the ratecoefficients of $\rm C_3H_3^+ + e^- \longrightarrow C_3H_2 + H$ for cyclic andlinear $\rm C_3H_2$ must be $\sim 20$ in order to reproduce the observations,depending on the branching ratios assumed for the $\rm C_3H_3^+ + e^-\longrightarrow C_3H + H_2$ reaction. In current astrochemical networks it isassumed that cyclic and linear $\rm C_3H_2$ are formed in a 1:1 ratio in theaforementioned reactions. Laboratory studies and/or theoretical calculationsare needed to confirm the results of our chemical modeling based onobservational constraints.

Understanding the $\rm C_3H_2$ cyclic-to-linear ratio in L1544