Density functional theory with the B3LYP functional is used to calculate the equilibrium geometries and harmonic vibrational frequencies of nitryl halogenides XNO_2 and XONO (X = F, Cl, Br, I). Satabilities and isomerizations of these isomers are investigated. Dissociation energies of the X-N bond in XNO_2 are predicted at the B3LYP/6-311G~* and QCISE(T)/cc-pvTZ levels. The electronic transition energies of the most stable XNO_2 species have been estimated by time- dependent B3LYP calculations. The electron promotion of a nonbonding electron of the halogen atom X in XNO_2 into a π~* orbital on the NO_2 moiety, i.e., the n→σ~* electron excitation, is responsible for the photodissociation of the X-N bond.

Key words: HALOGEN, NITROGEN OXIDE, AB INITIO CALCULATION, spectral characteristics, CONFIGURATION, EXCITED STATE, PHOTOINDUCED