How do complex organics and aromatic molecules form in cold clouds?
In plain words
Radio telescopes have found large ring-shaped carbon molecules and other complex organics in a dark cloud only about 10 degrees above absolute zero. Chemistry models predict far smaller amounts than are seen.
Precise statement
In TMC-1 (T ~ 10 K, n_H2 ~ 1e4 cm^-3) radio spectroscopy has detected complex organic molecules and cyano-substituted polycyclic aromatic hydrocarbons (cyanonaphthalenes, 2021; cyanopyrene, 2024; cyanocoronene, 2025) at abundances orders of magnitude above bottom-up gas-grain models. Identify the formation pathways (barrierless gas-phase growth, grain-surface chemistry with nonthermal desorption, or inheritance from an earlier phase) that reproduce the observed abundances.
What would settle it
A chemical network with laboratory-measured rate coefficients that reproduces the observed PAH and organic abundances in TMC-1 at its estimated age.