Defects in graphene sheets have been introduced by 500 keV C+ ion irradiation and have been studied by Raman spectroscopy. We have found marked differences in the vibrational behaviour for the irradiation of single layers, bilayers and multilayers which have been assigned to differences in the formation and evolution of damage. DFT calculations performed on circumcoronene monomer and its parallel dimers and trimers are in excellent agreement with the experimental results suggesting that graphitic islands of dimension comparable with circumcoronene can be obtained after the irradiation. The experimental and calculated Raman spectra have shown a blue shift of the D line by adding a second and a third layer to single layer graphene. This has been attributed to the energy interaction between the planes.