EXPERIMENTAL-EVIDENCE FOR THE EXISTENCE OF THE PROTONITRONIUM DICATION (HONO2+) IN THE GAS-PHASE AND AB-INITIO MOLECULAR-ORBITAL CALCULATIONS OF ITS POTENTIAL-ENERGY SURFACE

As conjectured by Olah et al. (J. Am. Chem. Soc. 1992,114, 5608), the protonitronium dication (HONO2+) is indeed a viable molecule which can be generated in the gas phase by dissociative electron impact ionization of HNO3. Charge stripping of HONO.+ does not result in the formation of a detectable dication, as the vertical removal of an electron leads to a vibrationally hot HONO2+ Molecule which undergoes spontaneous Coulombic explosion to generate H+ and NO2+. The kinetic energy release associated with this fragmentation has been determined experimentally to T(k) = 3.48 eV. State-of-the-art ab initio MO calculations of the complete active space SCF/multireference CI type are used to calculate the relevant parts of the potential energy surface of HONO2+, including its transition structures for the two charge separation reactions, i.e. formation of H+/NO2+ and OH+/NO+. Special emphasis is paid to the recently described model of Gill and Radom (J. Am. Chem. Soc. 1988, 110, 5311; Chem. Phys. Lett. 1988, 147, 213) for deprotonation of dications, and a detailed analysis is provided to explain why this, otherwise useful, approach is not applicable in the present system.