264 research outputs found
Cationic double K-hole pre-edge states of CS2 and SF6
Recent advances in X-ray instrumentation have made it possible to measure the
spectra of an essentially unexplored class of electronic states associated
with double inner-shell vacancies. Using the technique of single electron
spectroscopy, spectra of states in CS2 and SF6 with a double hole in the
K-shell and one electron exited to a normally unoccupied orbital have been
obtained. The spectra are interpreted with the aid of a high-level theoretical
model giving excellent agreement with the experiment. The results shed new
light on the important distinction between direct and conjugate shake-up in a
molecular context. In particular, systematic similarities and differences
between pre-edge states near single core holes investigated in X-ray
absorption spectra and the corresponding states near double core holes studied
here are brought out
Abiotic molecular oxygen production -- ionic pathway from sulphur dioxide
Molecular oxygen, O, is vital to life on Earth and possibly on other
planets. Although the biogenic processes leading to its accumulation in Earth's
atmosphere are well understood, its abiotic origin is still not fully
established. Here, we report combined experimental and theoretical evidence for
electronic-state-selective production of O from SO, a major chemical
constituent of many planetary atmospheres and one which played an important
part on Earth in the Great Oxidation event. The O production involves
dissociative double ionisation of SO leading to efficient formation of the
O ion which can be converted to abiotic O by electron neutralisation.
We suggest that this formation process may contribute significantly to the
abundance of O and related ions in planetary atmospheres, especially in
those where CO, which can lead to O production by different mechanisms,
is not the dominant component
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