Water dimers could abound in the atmosphere


Water dimers detected in atmospheric conditions

Mar 4, 2013

Physicists in Russia are the first to detect water dimers – bonded pairs of gaseous water molecules – in conditions similar to Earth’s atmosphere. Such dimers have been predicted to have important effects on the Earth’s radiation balance and atmospheric chemistry, so this latest breakthrough could help scientists gain a better understanding of how their presence affects climate.

Water vapour is the third most common gas in the Earth’s atmosphere, and the principal absorber of both sunlight and the Earth’s blackbody radiation. Scientists have known for decades that water appears to absorb more radiation than theoretical models suggest that it should. In the 1960s the Russian astronomer Sergei Zhevakin suggested that this discrepancy could be explained if, among the free water molecules (monomers), hydrogen bonding caused a small proportion of water molecules to pair-up to create dimers. These dimers, suggested Zhevakin and others, would be much stronger absorbers than single water molecules.

While chemists have been able to study water dimers at temperatures near absolute zero, it was not clear whether the structures could even form under conditions found in the Earth’s atmosphere. This is because the infrared spectral signatures of a dimer are extremely difficult to separate from those of single water molecules – making standard spectroscopy techniques unable to answer the question.

Read more: Water dimers detected in atmospheric conditions – physicsworld.com.

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