Scientists observe electron transitions in exploding molecules

Scientists observe electron transitions in exploding molecules

11:40 AM, 18th July 2014
Scientists observe electron transitions in exploding molecules
Artist’s impression of an exploding Iodomethanmoleküls with its electrons. © SLAC National Accelerator Laboratory.

HAMBURG, GERMANY: An international research team has observed electron transitions in exploding molecules with the help of ultra-short X-ray flashes. The study shows maximum distance to which a charge transfer takes place between the two fragments of a molecule. With the technique used allows the dynamics of charge transfer study in a wide range of molecular systems. Such processes play a role in many chemical processes, such as photosynthesis.

“Charge transfer takes place until around for ten times the normal bond length instead,” said Dr, Benjamin Erk, Researcher, DESY at the free-electron laser FLASH and at the Center for Free-Electron Laser Science (CFEL), a collaboration of DESY, Hamburg University and the Max . -Planck Society.

“A key question is: when is a molecule, a molecule. In this case, maximum distance to which the molecular constituents share the electrons, from what distance breaks the charge transfer between the two molecular fragments together. We measured critical distance marks the transition from molecular to atomic regime,” said Prof. Artem Rudenko, Kansas State University.

For their study, the researchers bombarded molecules of iodine and a methyl group (CH3), so-called iodomethane (CH3I), with an infrared laser and so broke the bond between the two partners. “With the help of ultrashort X-ray flashes, which also beat electrons from the inner shells of the iodine atoms, we could then watched as the shared electrons of shattering molecule between the two fragments is distributed,” said Dr Daniel Rolles, who heads a research group at DESY. The researchers currently the world’s most powerful X-ray laser LCLS at the US SLAC National Accelerator Laboratory in California.

“We have the X-ray flash behind somewhat later sent the infrared laser pulse at every step,” said Erk. This delay was between a few femtoseconds and a picosecond, ie up to a trillionth of a second. “The later the X-ray flash is, the farther the two molecular constituents already apart. In this way, the scientists won a series of recordings on which the migration of the electrons can be observed in ever greater separation between the molecular debris,” added Erk.

“The further removed the fragments, the more will the charge transfer from. We were up to a distance of about 20 angstroms electron migration between the two fragments of evidence,” said Erk. The bond length of iodomethane is, however, only slightly more than 2 angstroms, or 0.2 nanometers (millionths of a millimeter).

“Our results are for a number of systems of meaning. So you have about observed in astrophysics x-ray radiation generated by such charge transfer processes. Such processes play in many chemical processes involved, such as in photosynthesis or in solar cells. And in the research, scientists who study with X-ray radiation biomolecules to fight with radiation damage to their samples,” said Rudenko.

These initial results suggest also a bridge between the study of charge transfer between single atoms and the analysis of the electric charge flow in larger systems such as occur frequently in biology and chemistry. Further measurements should help to understand the process of charge transfer in detail.

© Deutsches Elektronen-Synchrotron News

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