Ab initio calculations on ONOOH and ONOO −

The geometry and electronic structure of peroxynitrous acid (ONOOH) and peroxynitrite ion (ONOO − ) were studied at the 6–31G ** level. The cis ‐configuration of peroxynitrous acid was found to be more stable by 3.9 kJ/mol than the trans ‐form, whereas peroxynitrite is more stable by 4.6 kJ/mol in the trans ‐form. Calculations of the skew forms, which are as defined by an angle of 90° between the ONO/NOO planes, yield energies larger than those of the most stable forms of the acid or anion by 51.4 and 68.1 kJ/mol, respectively, thus providing an estimate of the gas‐phase energy barrier. The electronic structure is discussed from the point of view of the reactivities and transformation processes of ONOOH and ONOO − . © 1993 John Wiley & Sons, Inc.