In the process of ozone hole formation, polar stratospheric clouds (PSCs) play an essential role. To understand the formation and the character of PSCs, we have carried out quantum chemical calculations on the N~2O~5 + H~2O reaction system, using different calculation methods. At the QCISD(T)//MP2/6-311 G(d,p) level, it is found that for the gas-phase reaction △H^0= - 39.5kJ·mol^-^1, △G^0= - 36. 1kJ/mol, E~a=88.2 kJ·mol^-^1 and 298K, respectively. These results are consistent with the facile hydrolysis of N~2O~5 by moisture.

Key words: NITRIC ANHYDRIDE, AB INITIO CALCULATION, WATER, ACTIVATION ENERGY