Diiodofuroxan (3,4-diiodo-1,2,5-oxadiazole 2-oxide) has been investigated for the first time in the gas phase by UV photoelectron spectroscopy, and in the solid phase by mid-infrared and Raman spectroscopy. The individual spectroscopies provide a detailed investigation into the vibrational and electronic character of the molecule, and are supported by quantum-chemical calculations. The molecule is confirmed by calculations at the B3LYP and CCSD(T) levels as a planar five-membered ring with a strong exocyclic and a relatively weak endocyclic N-O bond. Diiodofuroxan, upon thermolysis, does not cleave to the ICNO monomer, but leads to the formation of ONCCNO and iodine. (C) 2010 Elsevier B.V. All rights reserved.