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

Gaseous fluorodiazonium ions, FN2+, have been successfully obtained fr om the ionization of NF3/HN3 mixtures under typical chemical ionizatio n (CI) conditions, Using N-15-labeled hydrazoic acid, the formation of (FNN+)-N-15 ions is detected. The collisionally activated dissociatio n (CAD) experiments performed to probe the structures of FN2+ and (FNN +)-N-15 indicate that, in the latter species, the two nitrogen atoms a re not structurally equivalent. Thus, it is legitimate to identify the FN2+ ions as the linear F-N-N+, invariably predicted by all the avail able theoretical studies as the global minimum on the potential energy surface. The mechanism of formation of the fluorodiazonium ions has b een investigated by mass-analyzed ion kinetic energy (MIKE) and Fourie r-transform ion cyclotron resonance (FT-ICR) spectrometry, as well as by post-SCF ab initio calculations, up to the GAUSSIAN-1 level of theo ry. 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 C AD spectrometry. The details of this unimolecular decomposition have b een enlightened by combining the evidence from the MIKE experiments an d the results of the GAUSSIAN-1 ab initio calculations. The ion-molecu le reactions following the ionization of the NF3/HN3 mixtures have bee n also investigated by FT-ICR. In the low-pressure domain typical of t hese 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 domi nating species at long reaction times.