The equilibrium structures, vibrational spectra and relative energetics of (INO3) isomers have been investigated at the B3LYP, MP2 and CCSD(T) levels of theory, using the LANL2DZ methodology augmented with d and f polarization functions. The results indicate that iodine nitrate, IONO2, is by far the lowest energy structure while the cis-perp and trans-perp iodine peroxy nitrites, IOONO, are less stable by 31.6 and 34.2 kcal mol(-1), respectively, at the CCSD(T) level. The third isomer, OIONO, is found to be a bound minimum in both cis-perp and trans-perp conformations. (C) 2004 Elsevier B.V. All rights reserved.