Ultraslow isomerization in photoexcited gas-phase carbon cluster $${{\rm C}}_{10}^ -$$ C 10 -

Isomerization and carbon chemistry in the gas phase are key processes in many scientific studies. Here we report on the isomerization process from linear $${{\rm C}}_{10}^ -$$ C 10 - to its monocyclic isomer. $${{\rm C}}_{10}^ -$$ C 10 - ions were trapped in an electrostatic ion beam trap and then excited with a laser pulse of precise energy. The neutral products formed upon photoexcitation were measured as a function of time after the laser pulse. It was found using a statistical model that, although the system is excited above its isomerization barrier energy, the actual isomerization from linear to monocyclic conformation takes place on a very long time scale of up to hundreds of microseconds. This finding may indicate a general phenomenon that can affect the interstellar medium chemistry of large molecule formation as well as other gas phase processes.