Ethyl isocyanate-solvated magnesium cation complexes Mg+(OCNC2H5)(n) were produced in a laser-ablation supersonic expansion nozzle source. Photoinduced reactions in the complexes of Mg+(OCNC2H5)(n) (n = 1-3) have been studied as a function of the number of solvent molecules. Photodissociation action spectra of Mg+(OCNC2H5)(1-3) were recorded in the spectral range of 230-440 nm. Except for minor reactive products C2H5+ and Mg+OCN at short wavelengths from the photoreaction of the singly solvated complex Mg+(OCNC2H5), only evaporation products were observed from photodissociation of Mg+(OCNC2H5)(n) (n = 1-3). For all three complexes we studied, the ligands are believed to be in the first solvation shell. The action spectra of Mg+(OCNC2H5)(1-3) consist of two or three peaks on the red and blue sides of the Mg+ 3 (2)p <-- 3 S-2 atomic transition. The ground-state georrietries of Mg+(OCNC2H5)(1-3) were fully optimized at the B3LYP/6-31+G** level by using the GAUSSIAN 98 package. The absorption spectra of the complexes Mg+(OCNC2H5)(1-3) were calculated by using the optimized structures of their ground states with the CIS/6-31+G** method. The theoretical predictions appear to be consistent with the experimental results. An sp hybridization mechanism was proposed for the complexation of Mg+ and OCNC2H5, which results in the formation of big pi bonds between the magnesium cation and the ethyl isocyanate molecule, and further rationalizes the nearly linear backbone of Mg+-O-C-N-C in the complex Mg+(OCNC2H5).