RATIONALE: Sulfur hexafluoride (SF₆) being a potential greenhouse gas, coupled with its numerous applications, makes the study of the formation and fragmentation of SF_6^- based species important. The formation of SF₆- based anionic species has been studied using the gas feed-sputtering route and the mechanisms at play during the sputter-ejection of guest molecule-derived particles have also been probed.

METHODS: Studies of the formation of SF_n^– (n = 1–6) anions were conducted from various surfaces (metal and compound) that were subjected to Cs⁺ ion sputtering in the presence of SF₆ gas employing the gas feed-cesium sputter technique. The anions generated were mass analyzed using a double-focusing magnetic sector mass spectrometer. Quantum mechanical computations were performed to study the ground state structure and stability of neutral and negatively charged SF_n (n = 1–6) systems applying density functional theory (DFT) and ab initio methods (MP2 and CC).

RESULTS: This technique readily generated ³²SF_n^– (n = 1–6) anions for all sizes of ’n’ with practicable yields. Mass spectrometric measurements of the yield of sputter-ejected ³²SF_n^– (n = 1–6) anions reveal an oscillatory pattern as a function of ’n’, with odd values of ’n’ being relatively more abundant. The relative yield of ³⁴SF_n^– (n = 1–6) anions with respect to size was also measured albeit with low signal intensity. Also observed were F^–, S^–, F₂^–, ³³SF₅^– and ³³SF₆^–anionic species. The relevant electron affinity and bond dissociation energy (BDE) values were also computed.

CONCLUSIONS: Gas-phase SF_n^– (n = 1–6) anions can be effectively generated by using the gas spray-cesium sputter technique. Both experimental measurements and calculations indicate the existence of odd–even oscillations in the stability and electronic structure of the SF_n (n = 1–6) systems. The highest yield recorded was for the sputter-ejected SF₅^– species and this may be attributed to its ’superhalogen’ anionic character coupled with the relatively favorable F⁰ fragmentation pathway of sputtered SF₆^–. A signature pertaining to intact SF₆^– anion ejection is also observed.