Navigating Chemical Space through Isomerization Networks and Intermolecular Encounters of Seven Five-Atom Organic...

Theoretically unraveling the mechanisms of conformational interconversion is essential for elucidating isomeric formation and properties. For astrochemical species, these conformational dynamics represent a fundamental area of investigation, with significant implications for astronomical detection and laboratory studies. This study presents a systematic computational framework combining thermodynamic, kinetic, and dynamic analyses to map comprehensive reaction networks applicable to low-temperature environments. Using anharmonic downward distortion following (ADDF) algorithm, we constructed global isomerization route maps for seven key five-atom interstellar molecules: carbodiimide [HNCNH], cyanoacetylene [HC₃N], cyclopropenylidene [c-C₃H₂], methanimine [H₂CNH], formic acid [HC-(O)-OH], ketene [H₂C₂O], and protonated cyanogen [NCCNH⁺]. Our thermodynamic analysis identified 68 equilibrium structures, 208 transition states, 97 dissociation channels, and their interconnections across all species. Kinetic rate constant predictions incorporating quantum tunneling corrections reveal accessible exothermic patwhays from higher-energy to lower-energy isomers at cold environments. Complementary MC-AFIR exploration of bimolecular reactions between these species and five abundant small molecules (HF, HCl,H₂O, HCN, NH₃) generated ∼20,000 candidate products, with Born-Oppenheimer molecular dynamics validation confirming 37 distinct species as dynamically stable. This integrated approach reveals previously unrecognized molecular candidates and provides essential data for astronomical observations and astrochemical modeling, advancing our fundamental understanding of chemical complexity in diverse cold environments.