A radical route to interstellar propylene formation

Abstract

Complex organic molecules, such as propylene (CH3CHCH2), are detected in molecular clouds (such as TMC1) with high fractional abundances (~2×10-9, relative to hydrogen) that cannot be explained by gas-phase chemical reactions under normal dark-cloud conditions. To obtain such high abundances requires an efficient grain-driven chemistry to be operating, coupled with effective desorption of the complex organics back into the gas phase. We propose that the mechanism that we have previously describe- rapid high-density gas-phase chemistry in the gas released following sudden, total, ice mantle sublimation - can explain the high abundances, without recourse to ill-defined surface chemical pathways. Our model provides a natural explanation for why it is that some sources harbour high abundances of propylene, whilst others do not, based on the age and level of dynamical activity within the source (which affects the ice composition), and the chemical composition of the ambient gas. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.