Chemistry in Extreme Environments: The Mystery of Molecular Complexity in Space

Molecular complexity in the interstellar medium (ISM) poses one of the most intriguing challenges in astrochemistry: how can chemical reactions operate efficiently under the extreme physical conditions of space? In this Outlook, we summarize recent advances in understanding the molecular synthesis in the ISM, emphasizing the interplay between gas-phase and grain-surface chemistry. Laboratory studies, ranging from gas-phase kinetics at low temperature to the irradiation of interstellar ice analogues, demonstrate that both energetic and nonenergetic processes contribute to the formation of complex organic and prebiotic molecules. We discuss how accurate exploration of reactive potential energy surfaces by means of quantum-chemical methodologies combined with kinetic simulations provide an atomistic interpretation of the interstellar processes. Despite the advances of the past decade, interstellar chemistry remains in its infancy: reaction networks are incomplete, and quantitative predictions remain limited.