CHNO-CHNOS molecular network: (a) molecular network of 1669 molecular formulas (orange nodes = CHNO compounds, from Ar⁷⁺ -irradiated ice + red nodes = CHNOS compounds, from S⁷⁺-over-irradiated residue) illustrates the potential transformation of CHNO compounds toward CHNOS ones. Gray edges represent ΔCH₂, ΔH₂, ΔO, ΔH₂O, ΔNH and ΔCO₂, while ΔS transformations are shown in blue; (b) potential CHNOS precursors are significantly enriched in carbon number and double bond equivalent (DBE) compared to CHNO compounds that are not part of the CHNO-CHNOS molecular network. For reference, characteristics of PAHs (polycyclic aromatic hydrocarbons, dashed line) are indicated; (c) 29 potential direct CHNOS precursors (connected by ΔS transformations) show high N and C counts while having moderate numbers of O atoms per molecular formula (#N-#O-#C plot with bubble size scaled for 4 ≤ DBE ≤ 11).