SLAC researchers make movie of the first steps in a chemical reaction

Researchers have documented the ultrafast motion of electrons that drive the making and breaking of chemical bonds, including two processes never before captured on their natural timescales.

Key takeaways:
  • Researchers used SLAC’s X-ray laser to image early electron movement at attosecond timescales in what’s known as an “impulsively ionized” molecule. 
  • They captured two processes never before seen in real time: Coster-Kronig decay and quantum electron coherence. 
  • Experimental results contradicted leading computer simulations, forcing theorists to incorporate additional complexity for more accurate predictive models. 

All chemistry starts with a push from electrons. In the early moments of a chemical reaction, it’s the movement of electrons that initiates the breaking of old chemical bonds and forging of new ones, transforming one molecule into another.  

When an electron is removed from a molecule faster than the molecule can react – called “impulsive ionization” – the other electrons in the molecule enter excited quantum states that evolve on ultrafast timescales. Scientists have long sought to map the ultrasmall, ultrafast electronic motions behind chemical reactions on their natural timescales.  

Now, researchers at the Department of Energy’s SLAC National Accelerator Laboratory have created a movie of early electron motion in an impulsively excited molecule. Each frame captures changes happening in mere attoseconds, just billionths of a billionth of a second. Their results, published in Nature Physics, map the early steps of a photochemical reaction, similar to the reactions that drive countless processes – from X-ray interactions in medical settings to cosmic ray collisions in the upper atmosphere. Their results reveal steps of these processes never before resolved in time.

Read more on the SLAC website

Lasing achieved with hard X-rays in a resonator

Novel “XFELO” laser system produces razor-sharp X-ray light

For the first time, researchers have amplified X-ray light multiple times in a resonator cavity, in a way highly similar to traditional lasers. With great success: the new technique delivers extremely energetic X-ray pulses for high-precision experiments. This development opens up entirely new possibilities for research in physics, chemistry, or biology. The system is called “XFELO”. Researchers from European XFEL, DESY and Hamburg University have published their findings in the latest edition of the journal Nature. 

The team of engineers and scientists have shown for the first time that a hard-X-ray cavity can provide net X-ray gain, with X-ray pulses being circulated between crystal mirrors and amplified in the process, much like happens with an optical laser. The result of the proof-of-concept at European XFEL is a particularly coherent, laser-like light of a quality that is unprecedented in the hard X-ray spectrum. Lasing inside a cavity had been challenging to achieve with short-wavelength X-rays for a variety of reasons, including – on a basic level – that the nature of the light makes it difficult to reflect the beam at large angles. The “XFELO” (short for: X-Ray Free-Electron Laser Oscillator) technique opens new perspectives for scientific investigations, from ultrafast chemical reactions to detailed analyses of the smallest biological structures.

Read more on the European XFEL website

Image: Illustration of the XFELO system: a hard X-ray pulse (red) is reflected by a set of diamond mirrors and oscillates through arrays of magnets, so called undulators. On each roundtrip the pulse meets a new electron bunch (blue), which emits X-rays while passing through the undulators on a slalom course.

Credit: European XFEL