Abstract— Photoisomerization and photooxygenation of all-trans retinal in acetonitrile, illuminated by laser radiations (λact, = 333.6 or 350.7 nm), were investigated under various experimental conditions. In deoxygenated solutions, the major photoproducts are 13-cis and 9-cis retinal. All-trans and 13-cis 5,8-peroxyretinal are obtained in large amounts in oxygenated solutions. 11-cis derivatives have not been detected in any of these solutions. The photoproducts were identified by UV, NMR, mass and vibrational spectroscopies and HPLC chromatography. All-trans and 13-cis 5,8-peroxyretinal were isolated. Their vibrational spectra (IR and Raman) are analyzed. Most of the bands are assigned by comparison with previous studies on all-trans and 13-cis retinal, (E,E,E)-3-methyl-2,4,6-octatrienal and peroxides.