Computational insights into the chemical reaction networks of C ₃ H ₆ O ₃ , C ₃ H ₇ O ₃ and C ₂ H ₅ O ₂ : implications for the interstellar medium

The formation of complex organic molecules (COMs) in the interstellar medium (ISM) is central to astrochemistry and prebiotic chemistry, as these species may act as precursors to biomolecules essential for life. Among COMs, glyceraldehyde (HOCH₂CH(OH)C(O)H, GCA) has attracted attention as a potential building block in early biochemical pathways. Although GCA has not yet been detected in the ISM, the presence of structurally related compounds in various astronomical environments suggests that it may form under interstellar conditions. In this study, we employed the automated reaction discovery tool AutoMeKin to systematically explore the gas-phase chemical reaction networks (CRNs) of C₃H₆O₃ (GCA), C₃H₇O₃ (a hydrogenated analog), and C₂H₅O₂. Reaction pathways were characterized at the ωB97XD/Def2-TZVPP level of theory, and rate coefficients for key processes were computed using the competitive canonical unified statistical (CCUS) model, which accounts for multiple dynamic bottlenecks. Our analysis revealed several barrierless pathways leading to GCA or to GCA and a leaving group. Notably, the reaction between glyoxal (HCOHCO) and the HOCHCH₂OH radical, though neither has yet been detected in the ISM, was found to efficiently produce GCA and a formyl radical, with rate coefficients on the order of 5.4-7.9 × 10^-10 cm³ molecule^-1 s^-1 across the 10-100 K temperature range. However, aside from the aforementioned exception, most GCA formation channels result in highly vibrationally excited intermediates that are more likely to undergo rapid unimolecular decomposition than to be stabilized by radiative emission under typical ISM conditions. These results suggest that while gas-phase GCA formation is chemically feasible, it is likely transient and difficult to detect directly. In contrast, alternative products such as formaldehyde, glycolaldehyde, and (<i>Z</i>)-ethene-1,2-diol dominate many pathways and align better with current astronomical observations. This work provides detailed mechanistic and kinetic insights that enhance astrochemical modeling and advance our understanding of molecular complexity in star-forming environments. Furthermore, it highlights the utility of automated CRN exploration for uncovering viable synthetic routes to prebiotic molecules in space.