The purpose of the experiment was to observe the flow of crystals in the dissolved state on the micrometer scale, while other researchers have used LCLS to photograph the molecular motion in the gas. In 2015, they produced a “movie” of ring-shaped molecular breakages, which is a classic reaction in chemistry and biochemistry (see figure “Open Day”). The wavelength of X-rays is too long to directly capture atoms, so the research team relies on theoretical calculations to decompose the image into 16-frame molecular “movies”. At present, the new equipment worth 1 billion US dollars LCLS-II is under construction, and is expected to provide shorter wavelength X-rays, that is, faster pulse frequency, and further improve the time and spatial resolution of “movie”.
Open Day: An animation based on X-ray free electron laser (XFEL) measurements shows how a ring-shaped molecule breaks open on the femtosecond scale. It is hoped that the production of a new generation of small X-ray free electron laser pointer is expected to cost less than US $ 15 million each, which will allow more scientists to use these lasers. She is working with two collaborators to work on two prototype devices, and claims to complete the first one next year-called AXSIS, this device will be placed in the German Electronic Acceleration Center in Hamburg, Germany. These benchtop lasers can provide X-ray pulses as short as a few seconds, which means that the pulses will not destroy the target molecules.
Attosecond X-ray pulses emitted by small X-ray free electron lasers do not contain enough photons to obtain a clear image of each molecule, just like taking pictures in low light. At present, researchers are discussing a new idea to input X-rays or electron beams from a small green laser pointer or both into large devices such as SLAC to obtain brighter images. If this method does allow XFEL single molecule imaging, this “new camera” will be used to observe the most basic natural phenomenon: the moment when photons are absorbed by biological molecules and form excited states. “No one can see how fast this process is,” she said.
At present, the wavelength of the highest-energy X-ray in LCLS is 150 pm, which is slightly longer for resolving a single carbon atom or hydrogen atom. To have a higher spatial resolution, researchers need to use faster-moving electrons. Although cryo-electron microscopy can photograph multiple molecules at once, other techniques use electrons to image a single molecule. Last year, a research team led by the Barcelona Institute of Photonic Sciences in Spain proposed the use of laser excited electron diffraction (LIED) to study individual molecules of acetylene. In this technique, an infrared pulse illuminates the molecule from a specific direction, and then a second pulse knocks out two electrons in the molecule, breaking the covalent bond of carbon and hydrogen in the acetylene molecule.
Just like other forms of light, these red laser pointer pulses are formed by oscillating electric and magnetic fields. The electric field of the second pulse attracts a free electron and emits it back into the molecule. After the first escape, the electron returns after approximately 9 fs and quickly passes through the split molecules. Because of this, the diffraction of electrons is like waves breaking rocks on the coast, which can “freeze” the atomic position within a shutter time of less than 1 fs. This may be the ultimate version of the atomic “selfie”.
Whenever this process occurs, the electrons diffract in slightly different directions, so the team had to experiment over and over to collect enough data to build a clear image of the acetylene debris and the hydrogen ions that caused the acetylene to become debris. Each experiment was able to image a new molecule from the gas. After repeating it for about a billion times, the team has produced several frames of molecular “movies” that show covalent bond breaks. The team hopes to increase the number of frames as soon as possible to analyze more complex molecules.