A structural tranfsormation of C60 crystals has been induced by high fluence laser irradiation under various chemical environments. The role of oxygen in driving fullerene cage opening reactions is investigated. The resulting material, showing features typical of low density amorphous carbon, has been characterized by Raman spectroscopy. In order to provide an atomistic model of the damaged sample, we have simulated the irradiation process by a tight binding molecular dynamics calculation on a 240-atoms system. We have carefully investigated the structural and electronic properties. In particular, the short- and medium-range features have been related to the cage opening, which is here modeled as a sequence of bond breakings.