The mechanism of the reaction NH＋O~3→HNO＋O~2 has been studied by density functional theory (DFT) at the B3LYP method and 6－31+ +G^*^* level. The gemoetries of reactants, transition states, intermediates and products have been optimized and verified by frequency analysis. The relative single-point energies of the B3LYP/6－31+ +G^*^* structures have been calculated at the QCISD(T)/6－31+ +G^*^* level. The zero-point energy(ZPE) corrections were obtained. The results show that there are two reaction channels. The reactions of NH＋O~3 are electrophilic and strongly exothermic.

Key words: AB INITIO CALCULATION, OZONE, FREE RADICAL REACTION, TRANSITION STATE THEORY