Chiral H2S Ice

Spontaneous symmetry breaking and the emergence of homochirality have been long-standing mysteries in chemistry and physics. The observation of symmetry breaking in simple triatomic molecules, such as hydrogen sulfide (H2S), is challenging owing to rapid molecular motion and structural relaxation, it provides a fundamental yet poorly understood pathway to molecular handedness in the prebiotic universe.We reportthe firstexperimentalcharacterization of emergent chirality in H2S clusters using vibrational circular dichroism (VCD) in cryogenic matrices (4–40 K). By quenching molecular motion, we resolved a temperature-dependent structural bifurcation: at 10 K, H2S assembles into helical trimer-based strands, characteristic of amorphous ice,whereas at40 K, the system undergoes a cooperative reorganization into crystalline cage-like pentameric networks, characteristic of Phase III crystalline ice. Quantumchemicalsimulationsrevealedthatenthalpiccooperativityinthesethree-dimensional pentameric architectures through S–H⋯S hydrogen bonding and S⋯S interactions provides the criticalstabilizationrequiredforlong-rangecrystallineorder.Kineticanalysesfurther confirmed that the intrinsic chirality of the assemblies remained preserved due to cryogenic trapping, demonstrating the role of directional hydrogen-bonded supramolecular architectures insymmetrybreakingandprovidingexperimentalbenchmarksfortheoreticalmodels developed to treat chirality signatures and prebiotic life in interstellar icy mantles.