State selective fragmentation of doubly ionized sulphur dioxide

Abstract

Using multi-electron–ion coincidence measurements combined with high level calculations, we show that double ionisation of SO2 at 40.81 eV can be state selective. It leads to high energy products, in good yield, via a newly identified mechanism, which is likely to apply widely to multiple ionisation by almost all impact processes.

Abiotic molecular oxygen production—Ionic pathway from sulfur dioxide

“…The ion fragmentation curves are displaced horizontally on a common scale (with fixed offsets) and show true relative intensities, while the overall spectrum included for comparison has an intensity scale adjusted for display. The horizontal bar combs mark MRCI/aug-cc-pV(Q+d)Z computed vertical double-ionization energies of SO 2 quoted for C 2 v symmetry as given in ( 28 ).…”

“…Multiparticle coincidence experiments were carried out at 40.81-eV photon energy and a selection of solar soft x-ray line energies (about 88, 180, and 561 eV), which are well above the adiabatic single-photon double-ionization onset of SO 2 at 33.5 eV ( 27 ). The TOF-PEPEPIPICO apparatus used in the experiment has been described before ( 28 , 49 ). Briefly, it allows for continuous and simultaneous detection of multiple electrons with energy information and multiple cations with mass/charge information.…”

“…For the RCCSD(T) computations, we used the aug-cc-pV(5+d)Z basis set for sulfur and the aug-cc-pV5Z for oxygen. The energetics presented in this work were computed typically with an accuracy of about ±0.05 eV as known from benchmark calculations ( 28 , 64 ).…”

“…From previous studies [see ( 28 ) and references therein], it is known that upon double ionization SO 2 dissociates following four principal channelsnormalSO22+→O++normalSO+normalSO22+→O++S++normalOnormalSO22+→O2++S+normalSO22+→normalO+normalSO2+…”

“…A fifth channel producing two O + and a neutral S species is detectable but of negligible intensity. The other dissociative channels have been discussed in a previous publication ( 28 ), but here, we concentrate entirely on the formation of molecular oxygen ions.…”