Abstract: The photolysis of methyl nitrite has been theoretically studied. The ab initio and MP₂ calculations with STO-3Gbasis set show that both the S₀ and T₁ states of trans-CH₃ONO are more stable than the corresponding states of its cis-isomer. With the same method, the bond dissociation energies of the ground state,first excited (n→π^*) and second excited states (n→π^*) of CH₃ONO, withrupture of the bond between Nand Oatoms to producing CH₂O·and·NO radicals, are calculated to be 238.14, 68.99 and -183.97 kJ/mol, respectively, which supports the experimental fact that methyl nitrite is easy to proceed the photodecomposition. The photoelimination of the CH₃ONO (to produce CH,Oand HNOmolecules) is also investigated by ab inition and CIcalculations. The relationship of energies among S₀, T₁, S₁, T₂ and S₂ states along reaction path shows that the reaction rate of the photoelimination could not be fast, this is also in accord with the low quantum yield measured experimentally.

Key words: Methyl nitrite, Photolysis, Ab initio, CI