Proposed mechanisms for experiment 1.0. We note that all radical–radical reactions shown here are barrierless. Relevant species within each mechanism are boxed; solid-line boxes indicate stable species and dotted-line boxes indicate radicals. Species labelled with purple font are those that have been detected in space. Activation energies are by (a) Andersson et al. (2011), (b) Álvarez-Barcia et al. (2018), (c) Song & Kästner (2017), (d) Goumans & Kästner (2011), (e) Kobayashi et al. (2017), and (f) Zaverkin et al. (2018). An asterisk indicates the zero-point energy (ZPE) contribution.