August 4, 2010 | 17
The elusive goal of observing chemistry in action at the atomic level just took a quantum leap forward. Physicists using laser pulses have been able to observe for the first time—in real time—the outermost electrons of krypton atoms. As you may recall from high school chemistry it is these electrons that allow basic bonds to be made and broken—for example, the chemical binding of an oxygen atom with two hydrogen atoms to form water.
The key was using laser pulses lasting roughly 150 attoseconds (10 to the minus 18 of a second, or really, really, really, really short). First the physicists quickly ionized—or knocked one of the electrons off of—the krypton atoms with an infrared laser, according to a report summarizing the research in the August 5 issue of Nature. (Scientific American is part of Nature Publishing Group.) That "pump" was then followed rapidly by an ultraviolet laser probe that reveals the status of the hole that electron leaves behind. Do it a couple of times and you can find out exactly how the electron is moving and what it is getting up to, despite the fact that it is behaving as both a wave and a particle (what physicists like to call a wave-packet these days).
Such "attosecond transient absorption spectroscopy" as the physicists mellifluously call it should be able to observe—in real time—the formation of molecules, even compounds, and offers hope of showing how electrons actually behave when zipping through such a structure. That, in turn, might enable all sorts of new understandings of how chemistry works.
Of course, krypton itself is, generally speaking, chemically inert. So the method will have to be extended to other, more social atoms than the family of noble gases to really reveal something as well as to other phases, such as liquids and solids (something that seems feasible, according to the authors). Then scientists may finally see how and where a bond breaks or forms. But the technique has already shone a light on how an electron can still be entangled with the ion it has left behind—and might illuminate a path to a new understanding of the mechanisms behind chemical reactions.
Image: © Thorsten Naeser, MPQ Atoms of Krypton contained in gas cell that is placed into a vacuum chamber are exposed to an intense laser pulse to generate ions (blue jet). The interaction triggers coherent electron motion that is being captured by an attosecond pulse.