Cosmic benzene can’t form as predicted

When G. Stephen Kocheril started as a research associate at Jila, his first project was to experimentally test a decades-old theoretical reaction pathway for interstellar benzene formation. He was surprised by the result : the reaction terminated before benzene was produced ( Nat. Astron. 2025, DOI: 10.1038/s41550-025-02504-y). On March 26 at the ACS Spring 2025 meeting, Kocheril explained how he came to this unexpected conclusion. Researchers have long assumed that benzene is a precursor to interstellar polycyclic aromatic hydrocarbons (PAHs) , molecules that scientists think act as reservoirs of cosmic carbon . Benzene formation is considered a rate-limiting step of PAH formation and is a cornerstone of some mathematical models that predict PAH concentration. In the late 1990s, scientists proposed that ion-molecule collisions could be one way benzene forms. Kocheril wanted to test the proposed mechanism experimentally. “We’ve been able to prepare a laboratory environment where you can actually monitor