Onset of carbon cluster formation inferred from light emission in a laser-induced expansion

Space-time analysis of the light emitted from C, C₂, and C₃ has been performed in a laser-evaporated carbon expansion. The measured propagation velocities and concentration evolutions display the aggregation process as a half-collision governed by momentum conservation. C₂ and C₃ clusters are produced with strong electron excitation, the energy excess of which is removed by photon emission instead of collisional cooling.