ION-MOLECULE REACTIONS WITH S2F10 - DETECTION OF S2F10+, S2F11+ AND 2 ISOMERS OF SF5+

The chemical ionization of S2F10 has been investigated with measurements of ion/molecule reactions between S2F10 and the ions Ar.+, CO2.+, SO2.+, HBr.+, C2H2.+ COS.+, C-60(.3+) and C-60(2+) using the selected-ion flow tube (SIFT) technique at 294 +/- 2 K in helium at a total pressure of 0.35 Torr. S2F10.+, SF5+, SF3+ and S2F6.+ were observed as primary product ions with all reagent ions except C-60(n+). The occurrence and failure of charge transfer were used to bracket IE(S2F10) = 11.25 +/- 0.15 eV and to provide DELTAH(f,298)-degreees (S2F10.+) = -221.7 +/- 8.5 kcal mol-1. Two states of SF5+ of different chemical reactivity were identified and tentatively ascribed to square pyramid and trigonal bipyramid isomers. The SF5+ produced in the nearly thermoneutral charge-transfer reaction with COS.+ is seen to react further with S2F10 by F+ transfer to produce S2F11+ and is proposed to have a trigonal-bipyramid (D3h) Structure, while the SF5+ produced at high excess energies which reacts with S2F10 to produce SF3+ rather than S2F11+, is proposed to have a higher-energy square-pyramid (C4v) structure. With regard to the detection of S2F10 by chemical ionization, the experimental results demonstrate that S2F10.+ (and S2F6.+) ions can be formed in trace amounts from S2F10 by charge-transfer chemical ionization in helium at 294 +/- 2 K. Also, it is suggested that F+ transfer to produce S2F11+, as observed with SF5+, might be generally suited for the detection of S2F10.