Free Electron Laser Study of free carbon clusters

UV absorption from carbon nanoparticles is a very interesting astrophysical topic. The prominent hump centred at 217.5 nm is the most dominant feature in the interstellar extinction curve and also the most controversial and a long-standing problem in astrophysics. At the University of Milano an experimental set-up based on a Pulsed Microplasma Cluster Source has been developed for the investigation of free clusters at the Elettra Gas Phase beamline. The cluster source produces very intense cluster beams with tunable size distribution. The design of the apparatus is extended with a chamber for gas phase reaction (water vapour, CO, H2...) providing a unique opportunity to study the gas phase properties of carbonaceous particles in different environments. We plan to investigate Resonant Raman scattering of free carbon particles tuning the high brilliance UV/VIS storage ring FEL of ELETTRA across the region of 217.5 nm where the UV absorption hump in astrophysical data is observed and where a number of electronic transitions exist for variable size linear carbon chains.