The structure and photochemistry of the glyoxal-hydrogen peroxide complexes isolated in solid argon was studied by help of FTIR spectroscopy and quantum chemistry methods. The comparison of the experimental spectra with the MP2/6-311++G(2d,2p) calculated ones indicates that glyoxal-hydrogen peroxide complexes trapped in the matrix have cyclic structures; each subunit acts as a proton donor and a proton acceptor. Exposure of the complexes to the lambda > 345 nm radiation induces the addition reaction of hydrogen peroxide to glyoxal and formation of the 2-hydroxy-2-hydroperoxyethanal molecule. (C) 2009 Published by Elsevier B. V.