A methodology, which combines experimental evidence and theoretical calculations, able to give a molecular interpretation and a quantification of the photooxidation of polyolefins is here derived. The methodology involves the analysis of experimentally recorded infrared spectra in combination with density functional theory calculations. Environmental effects are taken into account by exploiting the polarizable continuum model. A test against polyethylene and polypropylene samples UV-irradiated under the conditions used for the photocoating is reported. The results obtained with the combined theoretical/experimental methodology are in good agreement with previous findings obtained by exploiting more complex purely experimental approaches.