Gk. Jarvis et al., A selected ion flow tube study of the reactions of several cations with the group 6B hexafluorides SF6, SeF6, and TeF6, J PHYS CH A, 104(46), 2000, pp. 10766-10776
The first investigation of the ion chemistry of SeF6 and TeF6 is presented.
Using a selected ion flow tube, the thermal rate coefficients and ion prod
uct distributions have been determined at 298 K for the reactions of 14 ato
mic and molecular cations, namely, H3O+, CF3+, CF+, CF2+, H2O+, N2O+, O+, C
O2+, CO+, N+, N-2(+), Ar+, F+, and Ne+ (in order of increasing recombinatio
n energy), with SeF6 and TeF6. The results are compared with those from the
reactions of these ions with SF6, for which the reactions with CF+, CF2+,
N2O+, and F+ are reported for the first time. Several distinct processes ar
e observed among the large number of reactions studied, including dissociat
ive charge-transfer and F-, F, F-2(-), and F-2 abstraction from the neutral
reactant molecule to the reagent ion. The dissociative charge-transfer cha
nnels are discussed in relation to vacuum ultraviolet photoelectron and thr
eshold photoelectron-photoion coincidence spectra of XF6 (X = S, Se, or Te)
. For reagent ions whose recombination energies lie between the first disso
ciative ionization limit (XF6 --> XF5+ + F + e(-)) and the onset of ionizat
ion of the XF6 molecule, the results suggest that if dissociative charge-tr
ansfer occurs, it proceeds via an intimate encounter. For those reagent ion
s whose recombination energies are greater than the onset of ionization, lo
ng-range electron transfer may occur depending on whether certain physical
factors apply, for example, nonzero Franck-Condon overlap. From the reactio
n kinetics, limits for the heats of formation (in kJ mol(-1)) of SeF4, SeF5
; TeF4, and TeF5 at 298 K have been obtained: Delta H-f degrees (SeF4) < -3
69, <Delta>H-f degrees (SeF5) < -621, <Delta>H-f degrees (TeF4) > -570, and
Delta H-f degrees (TeF5) < -822.