First step taken to image ultra-fast movements in chemical reactions

A team of international researchers have fired ultra-fast shots of light at oxygen, nitrogen and carbon monoxide molecules as part of a development aimed at mapping the astonishingly quick movements of atoms within molecules, as well as the charges that surround them.

The ultra-short laser that spans only a few hundred attoseconds -- an attosecond is equivalent to one quintillionth of a second -- was fired in a sample of molecules and could pave the way towards imaging the movement of atoms and their electrons as they undergo a chemical reaction -- one of the holy grails of chemistry research.

This latest study has been published today, 16 March, as part of a special issue on attosecond science, in IOP Publishing's Journal of Physics B: Atomic, Molecular and Optical Physics to mark the 10th anniversary of the first ever attosecond laser pulse.

Previous research has been able to probe the structure of molecules using a variety of techniques; however, the inherent challenge is to perform these experiments in systems where changes are rapidly occurring on very small time scales.

The researchers used two lasers in their experiments: the first held the molecule in place whilst the second was fired at it. The second laser operated in the extreme ultra-violet region of the electromagnetic spectrum as this is one of only two regions -- x-ray being the other -- where the laws of physics allow laser pulses to be produced on an attosecond timescale.

Once the target molecule was in place, short pulses of the laser were fired at in an attempt to dislodge an electron. This process, known as photoionization, allows atoms and molecules to be imaged in unprecedented detail as the ejected electrons carry crucial information about where it came from.

In this experiment, the samples, which existed as a gas, were stable, meaning no reactions were taking place; however, the major goal of the research team is to monitor the electrical and molecular changes, in real-time, that occur as atoms undergo a chemical reaction.

They intend to do this by triggering a reaction with the laser, breaking a chemical bond that holds molecules together, and then using the described technique to image the changes that occur in the molecule as they happen.

Lead author of the study Dr Arnaud Rouzée from the Max-Born-Institute said: "We show that the photoelectron spectra recorded for a small molecule, such as oxygen, nitrogen and carbon monoxide contains a wealth of information about electron orbitals and the underlying molecular structure.

"This is a proof-of-principle experiment that electrons ejected within the molecule can be used to monitor ultrafast electronic and atomic motion."

Story Source:

The above story is reprinted from materials provided by Institute of Physics (IOP), via AlphaGalileo.

Note: Materials may be edited for content and length. For further information, please contact the source cited above.

Journal Reference:

Arnaud Rouzée, Freek Kelkensberg, Wing Kiu Siu, Georg Gademann, Robert R Lucchese, Marc J J Vrakking. Photoelectron kinetic and angular distributions for the ionization of aligned molecules using a HHG source. Journal of Physics B: Atomic, Molecular and Optical Physics, 2012; 45 (7): 074016 DOI: 10.1088/0953-4075/45/7/074016

'Critical baby step' taken for spying life on a molecular scale

The ability to image single biological molecules in a living cell is something that has long eluded researchers; however, a novel technique, using the structure of diamond, may well be able to do this and potentially provide a tool for diagnosing, and eventually developing a treatment for, hard-to-cure diseases such as cancer.

In a study published May 19 in the Institute of Physics and the German Physical Society's New Journal of Physics, researchers have developed a technique, exploiting a specific defect in the lattice structure of diamond, to externally detect the spins of individual molecules.

Magnetic Resonance Imaging (MRI) has already taken advantage of a molecule's spin to give clear snapshots of organs and tissue within the human body, however to get a more detailed insight into the workings of disease, the imaging scale must be brought down to individual biomolecules, and captured whilst the cells are still alive.

Co-lead author Professor Phillip Hemmer, Electrical & Computer Engineering, Texas A&M University, said, "Many conditions, such as cancer and aging, have their roots at the molecular scale. Therefore if we could somehow develop a tool that would allow us to do magnetic resonance imaging of individual biomolecules in a living cell then we would have a powerful new tool for diagnosing and eventually developing cures for such stubborn diseases."

To do this, the researchers, from Professor Joerg Wrachtrup's group at the University of Stuttgart and Texas A&M University, used a constructed defect in the structure of diamond called a nitrogen vacancy (NV) -- a position within the lattice structure where one of the carbon atoms is replaced with a nitrogen atom.

Instead of bonding to four other carbon atoms, the nitrogen atom only bonds to three carbon atoms leaving a spare pair of electrons, acting as one of the strongest magnets on an atomic scale.

The most important characteristic of a diamond NV is that it has an optical readout -- it emits bright red light when excited by a laser, which is dependent on which way the magnet is pointing.

The researchers found that if an external spin is placed close to the NV it will cause the magnet to point in a different direction, therefore changing the amount of light emitted by it.

This change of light can be used to gauge which way the external molecule is spinning and therefore create a one-dimensional image of the external spin. If combined with additional knowledge of the surface, or a second NV nearby, a more detailed image with additional dimensions could be had.

To test this theory, nitrogen was implanted into a sample of diamond in order to produce the necessary NVs. External molecules were brought to the surface of the diamond, using several chemical interactions, for their spins to be analyzed.

Spins that exist within the diamond structure itself have already been modelled, so to test that the spins were indeed external, the researchers chemically cleaned the diamond surface and performed the analysis again to prove that the spins had been washed away.

Professor Hemmer continued, "Currently, biological interactions are deduced mostly by looking at large ensembles. In this case you are looking only at statistical averages and details of the interaction which are not always clear. Often the data is taken after killing the cell and spreading its contents onto a gene chip, so it is like looking at snapshots in time when you really want to see the whole movie."

"Clearly there is much work to be done before we can, if ever, reach our long-term goal of spying on the inner workings of life on the molecular scale. But we have to learn to walk before we can run, and this breakthrough represents one of the first critical baby steps."

Story Source:

The above story is reprinted (with editorial adaptations) from materials provided by Institute of Physics, via EurekAlert!, a service of AAAS.

Journal Reference:

Grotz et al. Sensing external spins with NV diamond. New Journal of Physics, 2011; [link]