H2NO2+ ions in the gas phase. A mass spectrometric and post-SCF ab initio study

Gaseous H2N02+ and CH4N02+ ions have been obtained by chemical ionization (CI), at pressures ranging from 0.2 to 0.4 Torr. Various reactions have been employed for the preparation of the H2N02+ ions, e.g., addition of water to nitrosonium ion, NO+, and protonation of ethyl nitrite and nitroethane by AH+ Bransted acids (A = H2 or CH4). The CH4N02+ ions have been obtained by addition of methanol to nitrosonium ion and by protonation of methyl nitrite by AH+ (A = CHI or H20). Structurally diagnostic mass spectrometric techniques, e.g., MIKE and CAD spectrometry, have been employed to probe the H2N02+ and CH4N02+ populations from the above reactions. Strong evidences have been obtained for the existence of two CH4N02+is omers, which have been assigned the (CH,-NOH)+ and (CH30H-NO)+ structures, whereas the single isomer detectable in the H2N02+ populations has been identified as the nitrosohydronium ion, (H20-NO)+. The results of molecular orbital calculations at the MP4(SDTQ)//6-31 lG**/MP2(FU)//&31G** + ZPE (MP2(FU)/6-31G**) post-SCF level of theory identify six different conformers of the H2N02+ ion as stable species (true minima on the surface), the nitrosohydronium ion being the most stable one. At the post-SCF level of theory, the latter species is viewed as an ion-molecule complex between NO+ and H20, rather than as a normal cation. Employing the Gaussian-1 theory, recently outlined by Pople and co-workers, a heat of formation of 160 * 2 kcal mol-' has been computed for this ion, which compares fairly well with the experimental heat of formation of the H2N02+ ion, 159 * 1.5 kcal mol-].