The intra-complex reaction in Mg+-nitromethane by photons in the spectral region of 240-400 nm has been studied. The product Mg+, Mg+O, Mg+OH, and Mg+NO2 were observed. The products Mg+ and Mg+OH appeared throughout the whole wavelength range, but the product Mg+O emerged only in the shorter wavelength region, whereas the product Mg+NO2 in the longer one. The calculated results show that there are the two isomers. The absorption spectrum of the two isomers were calculated, and the isomer, which is with Mg+ attached to single O atom, was in good agreement with the experimental data. On the basis of the branching fraction data, the orientation of the electronic orbital, and reaction energies, the photoreaction mechanisms were explained for the Mg+ insertion the chemical bonds and the state-specificity. (c) 2006 Elsevier B.V. All rights reserved.