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 report the first experimental characterization 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 at 40 K, the system undergoes a cooperative reorganization into crystalline cage-like pentameric networks, characteristic of Phase III crystalline ice. Quantum-chemical simulations revealed that enthalpic cooperativity in these three-dimensional pentameric architectures through S–H⋯S hydrogen bonding and S⋯S interactions provides the critical stabilization required for long-range crystalline order. Kinetic analyses further confirmed that the intrinsic chirality of the assemblies remained preserved due to cryogenic trapping, demonstrating the role of directional hydrogen-bonded supramolecular architectures in symmetry breaking and providing experimental benchmarks for theoretical models developed to treat chirality signatures and prebiotic life in interstellar icy mantles.