2026ApJ..1000...76W

Although oxygenated benzene derivatives are key precursors in the abiotic synthesis of biorelevant molecules and fundamental building blocks of functionalized polycyclic aromatic hydrocarbons, their formation mechanisms under interstellar conditions have remained largely unexplored. Here, we report the first bottom-up formation of phenol (C₆H₅OH) in low-temperature interstellar ice analogs composed of acetylene and water (C₂H₂-H₂O). Utilizing vacuum ultraviolet photoionization reflectron time-of-flight mass spectrometry and resonance-enhanced multiphoton ionization, phenol, along with aromatic hydrocarbons including benzene (C₆H₆), phenylacetylene (C₆H₅CCH), styrene (C₆H₅CHCH₂), naphthalene (C₁₀H₈), and phenanthrene (C₁₄H₁₀), were identified in the gas phase during temperature-programmed desorption. Among these species, styrene, naphthalene, and phenanthrene have not yet been detected in the interstellar medium, suggesting that they are suitable targets for future astronomical searches. These findings reveal viable low-temperature formation pathways for phenol through nonequilibrium chemistry in acetylene-containing interstellar ices, thereby advancing our understanding of the abiotic formation of oxygenated benzene derivatives in extraterrestrial environments.