Cold Chemistry, Hot Implications: Molecular Complexity in Interstellar Space

Speakers: Prof. Ralf Kaiser (University of Hawaii, W M Keck Center for Astrochemistry)

Over the past decade, a paradigm shift has emerged in astrochemistry: complex organic molecules can form efficiently in the coldest regions of space. Ice-coated interstellar grains are now recognized as molecular factories that drive the synthesis of biorelevant species within cold molecular clouds and star-forming regions—environments once thought too inert to sustain such chemistry.

Understanding this unexpected reactivity requires bridging gas-phase and condensed-phase processes. In this talk, we present molecular beam and surface science experiments that resolve the underlying reaction dynamics and kinetics. In the gas phase, we uncover pathways to polycyclic aromatic hydrocarbons (PAHs), the fundamental building blocks of carbonaceous nanoparticles. On icy grains, we demonstrate the formation of complex organics—including amino acids, sugars, and polyalcohols under conditions that challenge conventional assumptions about chemical stability and reactivity at low temperatures.

Our approach combines isomer-selective vacuum ultraviolet (VUV) photoionization with reflectron time-of-flight mass spectrometry (ReTOF-MS) and infrared (FTIR) spectroscopy, enabled by advanced VUV light sources such as four-wave mixing and synchrotron radiation. These methods provide unprecedented access to reaction mechanisms at the molecular level. The results reveal efficient, low-temperature routes to aromatic and complex organic molecules via non-classical pathways involving radical–radical reactions, submerged barriers, and excited-state dynamics. These findings overturn the long-held view that such molecular complexity requires high temperatures and instead point to a fundamentally different chemical regime operating in deep space. By exposing the mechanisms that govern carbon chemistry under extreme conditions, this work reframes our understanding of molecular evolution in the universe—and the origins of chemical complexity itself.

https://indico.phys.hawaii.edu/event/2761/