GASEOUS FLUORODIAZONIUM IONS - EXPERIMENTAL AND THEORETICAL-STUDY ON FORMATION AND STRUCTURE OF FN2+

Gaseous fluorodiazonium ions, FN2+, have been successfully obtained from the ionization of NF3/HN3 mixtures under typical chemical ionization (CI) conditions, Using N-15-labeled hydrazoic acid, the formation of (FNN+)-N-15 ions is detected. The collisionally activated dissociation (CAD) experiments performed to probe the structures of FN2+ and (FNN+)-N-15 indicate that, in the latter species, the two nitrogen atoms are not structurally equivalent. Thus, it is legitimate to identify the FN2+ ions as the linear F-N-N+, invariably predicted by all the available theoretical studies as the global minimum on the potential energy surface. The mechanism of formation of the fluorodiazonium ions has been investigated by mass-analyzed ion kinetic energy (MIKE) and Fourier-transform ion cyclotron resonance (FT-ICR) spectrometry, as well as by post-SCF ab initio calculations, up to the GAUSSIAN-1 level of theory. The FN2+ ions originate from the loss of HF from a F2N-NH+ moiety, detected as well in the CI plasma and structurally characterized by CAD spectrometry. The details of this unimolecular decomposition have been enlightened by combining the evidence from the MIKE experiments and the results of the GAUSSIAN-1 ab initio calculations. The ion-molecule reactions following the ionization of the NF3/HN3 mixtures have been also investigated by FT-ICR. In the low-pressure domain typical of these experiments, the gas-phase ion chemistry essentially consists of the fast electron transfer reactions from HN3 to NF3.+, NF2+, and NF.+. Protonated hydrazoic acid, H2N3+, is eventually observed as the dominating species at long reaction times.