This is how long the pair of electrons needs for one cycle of the pulsing motion in which the pair is initially closer to the nucleus, then moves away from it and then returns to the nucleus again. They succeed only because the duration of this pulse is shorter than one femtosecond (one-millionth part of a billionth of a second), however. The researchers first move the electrons of the helium into the ultrafast pulsing state with the aid of an ultraviolet flash. the colour of the pulses, which is important here, but also their intensity and the interval between them. In order to choreograph and film electrons in a helium atom, the Heidelberg-based physicists sent two laser pulses through a cell with helium gas. It is useful for chemistry, on the other hand, if they are able to direct pairs of electrons, because the typical chemical bond consists of just such a pair this means that chemists must always move at least two electrons when they want to create or break a molecular bond. On the one hand, the study of an electron pair is useful for physicists who want to gain a better understanding of how atoms and molecules interact with light as this interaction usually involves two or more electrons. “We have now achieved it for a pair of electrons which were bound together for a short time.” When electrons are shifted, molecular bonds can be created “The motion of individual electrons in the atom has already been imaged quite often and even manipulated as well,” says Christian Ott, lead author of the study. They laid down the rhythm of the electronic partner dance, so to speak. The researchers were not satisfied with the role of mere observers, however, and also actively intervened in the electronic choreography. They observed how the electron pair danced close to the atomic nucleus one moment and slightly moved away from it the next moment. It is precisely this pulsing motion that scientists working with Thomas Pfeifer, Director at the Max Planck Institute for Nuclear Physics, have recorded in a series of images of a helium atom. In some electronic states – physicists call them superposition states – this motion manifests itself as a pulsing with a regular beat. When electrons move, this brings about a change to the regions where the electrons have the highest probability of being located. Physicists cannot determine their precise location in an atom, but they can narrow down the region where the charge carriers are most probably located. Physicists aim to specifically influence the motion of electron pairs because they want to revolutionize chemistry: If lasers can steer the paired bonding electrons in molecules, they could possibly produce substances that cannot be produced using conventional chemical means.Įlectrons are hard to get a hold of. One attosecond corresponds to a billionth of a billionth of a second. They employed a combination of visible flashes of light and extreme-ultraviolet pulses which lasted only a few hundred attoseconds. The scientists are succeeding in this task with the aid of different laser pulses which they timed very accurately with respect to each other. A German-Spanish team working with researchers from the Max Planck Institute for Nuclear Physics in Heidelberg has now become the first to image the motion of the two electrons in a helium atom and even to control this electronic partner dance. Physicists are continuously advancing the control they can exert over matter. Using attosecond-timed laser flashes, a team of physicists has become the first to image and control the motion of the two electrons in a helium atom. At 16.3 femtoseconds they arrive back at their original position again they thus move with a beat of around one femtosecond. The color indicates the probability of finding one electron at position A (vertical axis) and the second electron at position B (horizontal axis) on a line drawn through the atom (along the polarization direction of the laser). At 15.3 femtoseconds (fs) the two electrons are close to the nucleus (center of image) and then move away from it. The close approach of the positive side of the dipole attracts the electron cloud toward it.Electronic pas de deux: Physicists in Heidelberg have filmed the pulsing motion of the electron pair in a helium atom. \): The polarization and attraction of a helium atom by a dipole.
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