2024ApJ...963..142G

Phosphorus monoxide (PO) is a key brick of prebiotic chemistry since it is a potential precursor of phosphates, which are present in all living systems. Prompted by the lack of information on the different processes involved in the formation of PO, we have revisited and analyzed in detail the P(⁴S) + O₂(³Σ^–) and P(⁴S) + O₂(¹Δ) reactions leading to PO. The former process has been widely studied from both experimental and theoretical points of view, however, with contradictory results. We have used high-level quantum-chemical calculations to accurately describe the reaction mechanisms. Next, rate constants have been computed using a master equation approach based on ab initio transition state theory. By incorporating the P(⁴S) + O₂(³Σ^–) reaction in an astrochemical model, we have found that this reaction cannot be overlooked when aiming at a complete understanding of the PO abundance in regions dominated by shocks with speeds below 40 km s^–1.