  Thanks to the Cassini Huygens mission, it is now established that the first
aerosols in Titan s upper atmosphere are found from an altitude of about 1200
km. Once they are formed and through their descent towards the surface, these
nanoparticles are submitted to persistent Far Ultra-Violet (FUV) radiation that
can reach lower atmospheric layers. Such an interaction has an impact,
especially on the chemistry and charge budget of the atmospheric compounds.
Models are useful to understand this photoprocessing, but they lack important
input data such as the photoemission threshold or the absolute
photoabsorption/emission cross sections of the aerosols. In order to quantify
the photoemission processes, analogs of Titan s aerosols have been studied with
the DESIRS FUV beamline at the synchrotron SOLEIL as isolated substrate-free
nanoparticles. We present here the corresponding ARPES (Angle-Resolved
PhotoElectron Spectroscopy) data recorded at different FUV photon energies. The
results show a very low photoionization threshold (6.0 +/- 0.1 eV~ 207 nm) and
very high absolute ionization cross sections (~106 Mb) indicating that FUV
photoemission from aerosols is an intense source of slow electrons which has to
be taken into account in photochemical models of Titan s atmosphere.
