Quantum weirdness can generate a molecule in space that shouldn't exist by the classic rules of chemistry. If interstellar space is really a kind of quantum chemistry lab, that might also account for a host of other organic molecules glimpsed in space.
Interstellar space should be too cold for most chemical reactions to occur, as the low temperature makes it tough for molecules drifting through space to acquire the energy needed to break their bonds. "There is a standard law that says as you lower the temperature, the rates of reactions should slow down," says Dwayne Heard of the University of Leeds, UK.
Yet we know there are a host of complex organic molecules in space. Some reactions could occur when different molecules stick to the surface of cosmic dust grain. This might give them enough time together to acquire the energy needed to react, which doesn't happen when molecules drift past each other in space.
Not all reactions can be explained in this way, though. Last year astronomers discovered methoxy molecules – containing carbon, hydrogen and oxygen – in the Perseus molecular cloud, around 600 light years from Earth. But researchers couldn't produce this molecule in the lab by allowing reactants to condense on dust grains, leaving a puzzle as to how it could have formed.
Molecular hang-out
Another route to methoxy is to combine a hydroxyl radical and methanol gas, both present in space. But this reaction requires hurdling a significant energy barrier – and the energy to do that simply isn't available in the cold expanse of space.
Heard and his colleagues wondered if the answer lay in quantum mechanics: a process called quantum tunnelling might give the hydroxyl radical a small chance to cheat by digging through the barrier instead of going over it, they reasoned.
So, in another attempt to replicate the production of methoxy in space, the team chilled gaseous hydroxyl and methanol to 63 kelvin – and were able to produce methoxy.
The idea is that at low temperatures, the molecules slow down, increasing the likelihood of tunnelling. "At normal temperatures they just collide off each other, but when you go down in temperature they hang out together long enough," says Heard.
Impossible chemistry
The team also found that the reaction occurred 50 times faster via quantum tunnelling than if it occurred normally at room temperature by hurdling the energy barrier. Empty space is much colder than 63 kelvin, but dust clouds near stars can reach this temperature, adds Heard.
"We're showing there is organic chemistry in space of the type of reactions where it was assumed these just wouldn't happen," says Heard.
That means the chemistry of space may be richer than we had imagined. "There is maybe a suite of chemical reactions we hadn't yet considered occurring in interstellar space," agrees Helen Fraser of the University of Strathclyde, UK, who was not part of the team.
However, just because these molecules can form in space doesn't mean that space is the origin of such molecules on Earth. "The jury is still out on that," she says.
Journal reference: Nature Chemistry , DOI: 10.1038/NCHEM.1692
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