PROTONATED NITRIC-ACID - STRUCTURE AND RELATIVE STABILITY OF ISOMERIC H2NO3+ IONS IN THE GAS-PHASE

Gaseous H2N03 + ions have been obtained from direct protonation of nitric acid by H3 +, CH5 +, and H30+ as well as from the protonation of C2H50N02 followed by C2H4 loss. The proton affinity of nitric acid has been estimated to be 168 ± 3 kcal mol-1 from the results of bracketing experiments carried out by FT-ICR and Cl mass spectrometry. Structural analysis by MIKE and CID spectrometry of H2N03 + ions and of their 18O-labeled isotopomers obtained from the exchange with H2 18O provides strong evidence for the existence of two isomers, characterized by the (HO)2NO+ and the H2O. NO2 + structure, and for the higher stability of the latter. The results are consistent with those of independent MO SCF calculations, pointing to the higher stability of the H2O. NO2 + structure. © 1990, American Chemical Society. All rights reserved.