Investigation of Gas-Phase Formation of Glycolaldehyde, Glyceraldehyde, and Dihydroxyacetone under Interstellar Medium Conditions

Abstract

Organic compounds, including sugars and their precursors, have been identified in the interstellar medium (ISM) and are of special prebiotic interest. Herein, we perform a detailed kinetic and thermodynamic analysis at CCSD(T)//M06–2X/aug-cc-pVTZ+ZPE level of three sugar precursors, glycolaldehyde (GA), glyceraldehyde (GLY), and dihydroxyacetone (DI), evaluating both their unimolecular degradation and formation pathways in the temperature range of 10–500 K. Our results reveal that all three species exhibit high activation energies for thermal fragmentation (E_a > 70 kcal mol^–1), which implies effective kinetic stability in cold environments (∼10K). This supports their possible persistence in dense molecular clouds and aligns with the mechanism proposed by [Yang, Z. Mol. Phys. 2024, 122, e2134832], where third-body collisions can stabilize reactive bimolecular complexes even at low temperatures. Among the formation routes investigated, the association of HCOH and H₂CO to form GA occurs predominantly through the barrierless abstraction of the hydroxylic hydrogen from trans-HCOH by carbonyl oxygen. Additionally, the thermal degradation indicates that DI exhibits a higher propensity for dissociation than its aldehydic counterparts (GA and GLY) above 100 K, although this difference diminishes at higher temperatures (>300 K), where their rates converge. These findings highlight the importance of integrating kinetic and thermodynamic data into astrochemical models to accurately assess the formation, survival, and destruction of organic molecules in different astrophysical environments.