In the cold Taurus cloud, where stars are born, telescopes have detected molecules with the smell of bitter almonds — aromatic nitriles. On Earth, you can find them in peach pits, but in space they hang in icy dust. What happens to them under the harsh ultraviolet light of young stars? Chemists recreated this process in the lab.

In a special chamber at minus 268 degrees Celsius, benzonitrile and its cousins were irradiated with ultraviolet light at a wavelength of 193 nanometers. The molecules fell apart, and the main fragments turned out to be hydrogen cyanide (HCN) and its isomer HNC — the very ones already found in space. This means that light strips a group containing nitrogen and carbon from the ring, leaving a bare benzene core.

Experiments with heavy hydrogen (deuterium) confirmed that the bond between the ring and the nitrile group breaks first, and only then do the fragments pick up hydrogen from the icy substrate. Such details help astronomers decipher the infrared spectra of distant clouds, where similar processes are happening right now.