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The high speed at which protons can travel during
chemical reactions means their motion needs to be measured in units of
time called 'attoseconds', with one attosecond equating to one
billion-billionth of a second. The team's observation of proton motion
with an accuracy of 100 attoseconds in hydrogen and methane molecules
is the fastest ever recorded. Dr John Tisch of Imperial College London
says:
"Slicing up a second into intervals as miniscule as
100 attoseconds, as our new technique enables us to do, is extremely
hard to conceptualise. It's like chopping up the 630 million
kilometres from here to Jupiter into pieces as wide as a human hair."
Professor Jon Marangos, Director of the Blackett
Laboratory Laser Consortium at Imperial, says this new technique means
scientists will now be able to measure and control the ultra-fast
dynamics of molecules. He says:
"Control of this kind underpins an array of future
technologies, such as control of chemical reactions, quantum computing
and high brightness x-ray light sources for material processing. We
now have a much clearer insight into what is happening within
molecules and this allows us to carry out more stringent testing of
theories of molecular structure and motion. This is likely to lead to
improved methods of molecular synthesis and the nano-fabrication of a
new generation of materials."
Lead author Dr Sarah Baker of Imperial College
believes that the technique is also exciting because of its
experimental simplicity. She says:
"We are very excited by these results, not only
because we have 'watched' motion occurring faster than was previously
possible, but because we have achieved this using a compact and simple
technique that will make such study accessible to scientists around
the world."
To make this breakthrough, scientists used a
specially built laser system capable of producing extremely brief
pulses of light. This pulsed light has an oscillating electrical field
that exerts a powerful force on the electrons surrounding the protons,
repeatedly tearing them from the molecule and driving them back into
it.
This process causes the electrons to carry a large
amount of energy, which they release as an x-ray photon before
returning to their original state. How bright this x-ray is depends on
how far the protons move in the time between the electrons' removal
and return. The further the proton moves, the lower the intensity of
the x-ray, allowing the team to measure how far a proton has moved
during the electron oscillation period. |
