Abstract: In this paper, the photorearrangement of nitromethane has been studied by ab initio SCF MO and CI (configuration interaction) calculations with STO-3G basis set. Potential energy contours of ground state and some excited states show that it is very difficult for nitromethane to rearrange into methyl nitrite because of the high barriers, either in photoreaction or ther-moreaction. The studies consist of the following steps: Geometries of reactants and products of S₀ states and n→π^* excited state (S₁, T₁) were calculated by using gradient method. Transition state (S₀) was optimized by minimizing the Euclidean norm of energy gradient. In order to investigate the photorearrangement of nitromethane, we have also calculated the potential contours of S₀ state, n→π^* excited state (S₁, T₁) and π→π^* excited state (S₂, T₂) with Cl method along the intrinsic reaction coordinate (IRC) of S₀ state. The conclusion we got by analyzing the results of calculation is in agreement with the recent experiment.

Key words: nitromethane, photorearrangement, quantum chemistry, configuration interaction