A New "Non-energetic" Route to Complex Organic Molecules in Astrophysical Environments: The C + H2O → H2CO Solid-state Reaction

The solid-state reaction C + H₂O → H₂CO was studied experimentally following the co-deposition of C atoms and H₂O molecules at low temperatures. In spite of the reaction barrier and absence of energetic triggering, the reaction proceeds fast on the experimental timescale pointing to its quantum tunneling mechanism. This route to formaldehyde shows a new "non-energetic" pathway to complex organic and prebiotic molecules in astrophysical environments. Energetic processing by UV irradiation of the ice produced by co-deposition of C and H₂O reactants leads mainly to the destruction of H₂CO and the formation of CO₂, challenging the role of energetic processing in the synthesis of complex organic molecules under astrophysically relevant conditions.