German researchers have identified experimentally H₂Si=S, a molecule thought to exist in outer space, for the first time.

A team led by Sven Thorwirth at the Max Planck Institute for Radioastronomy, Bonn, were able to characterise this elusive molecule using microwave spectroscopy. 'Cosmically, silicon and sulfur are very abundant elements,' says Thorwirth. This unsubstituted silanethione is 'a plausible astronomical molecule' that may exist in the shells of dust surrounding dying stars, he explains.

Several substituted silanethiones, RR'Si=S, stabilised by bulky alkyl (R) groups have already been synthesised and their structures determined using X-ray crystallography. But the unsubstituted silanethione - the second-row analogue of formaldehyde - had never been seen before.

Thorwirth used microwave spectroscopy - which measures the difference between the electromagnetic radiation absorbed by a molecule and that emitted - to look for the molecule.  The radiation difference is associated with the molecule's rotation, and is used to indentify molecular species and isotopes. The team then backed up their experimental results with high-level quantum chemical calculations.  Explaining the significance of this work, Thorwirth says that the 'data provide the laboratory basis needed for future radio astronomical searches for this molecule in space.'

The work is welcomed by Paul Davies, a member of the infrared laser spectroscopy group at the University of Cambridge, UK, who says that this combination of spectroscopy and high-level calculations 'should be generally applicable for unravelling the spectra from increasingly complicated molecules, hence enabling the full potential of microwave spectroscopy to be realised.' 

Vikki Chapman

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