Here’s the story in a nutshell:
Scientists have long known how to control the internal states of molecules, such as their rotational and vibrational energy levels. In addition, the field of quantum chemistry has existed for decades to study the effects of the quantum behavior of electrons and nuclei—constituents of molecules. But until now scientists have been unable to observe direct consequences of quantum mechanical motions of whole molecules on the chemical reaction process. Creating simple molecules and chilling them almost to a standstill makes this possible by presenting a simpler and more placid environment that can reveal subtle, previously unobserved chemical phenomena.
The new research started with the premise that in extreme cold – a few hundred billionths of a Kelvin (nanokelvins) above absolute zero (minus 273 degrees Celsius or minus 459 degrees Fahrenheit – no chemical reactions should occur.
The physicists at JILA (formerly the Joint Institute for Laboratory Astrophysics, now just JILA, a joint venture of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder, USA) cooled a gas of potassium and rubidium molecules to this temperature and subjected them to manipulation with electric fields. Then they observed the unexpected – heat – a few billionths of a degree to be sure, but measurable proof that chemical reactions were taking place and, in fact, taking place very quickly.
Taking the experiments further, the researchers worked with the gas as a 50/50 mix of molecules with two different ‘spins’ (that’s spin in the quantum sense, the angular momentum) and found that this increased the speed of reaction up to a hundred-fold. This is indicative that manipulating quantum properties (electronic, vibrational and rotational states) changes the chemical reaction.
How this works is still very much up for more research. These are ‘toe in the water’ experiments that only hint at what’s happening. Outside of masses of equations for the highly trained few, an intuition for molecular quantum chemistry are difficult to explain. I’ll try.
Here’s a crude analogy to work with: Consider two magnets, tiny bars with polar ends. We know that putting to unlike poles together and the bars attract each other. They repel each other when two like poles are put together. Simple magnetic properties. Now visualize these bars having unequal magnetic energy, one bar is more strongly magnetized than the other; that they are rotating very fast; spinning (with different total angles of momentum) so that the orientation of the poles continually changes, and that each bar is vibrating at different rates. What happens to the magnetic properties? How would these two bars react to each other? The quantum mechanics of molecules isn’t the same as this kind of magnetism, but perhaps this helps visualize how differently the magnets might behave when the extra conditions are added. That complex behavior is analogous to what it’s like for molecules undergoing quantum chemistry, and why, when scientists get their first glimpses of such behavior, they realize that underlying all that we think we know about chemistry, is another, more subtle but nevertheless decisive set of behaviors that governs how molecules react to each other.
I’m searching for a metaphor – a door opening, curtain rising, fog lifting – not really any of these. That there is such a thing as quantum chemistry, scientists have known for quite a while; but this…this is something else. It’s in between what we knew about individual nuclear particles and the much larger world of molecular chemistry (which itself is a smaller world inside the world we see as physical reality). We’re just beginning to get a fix on the existence of this ‘world’ of molecular quantum chemistry, and the minds of scientists boggle at the implications. For example, here’s a typically reserved statement from the research:
…a key to advancing biology, creating new materials, producing energy and other research areas. The new JILA work also will aid studies of quantum gases (in which particles behave like waves) and exotic physics spanning the quantum and macroscopic worlds. It may provide practical tools for “designer chemistry” and other applications such as precision measurements and quantum computing.
Is there anything this doesn’t cover? Not really. Quantum physics underlies everything, so unless its effects are trivial, it affects everything. The ability to manipulate quantum chemistry means that in some way, almost any kind of physical material or process is fair game. Among other things, just the other week scientists announced the discovery that plants are (since long ago) using quantum mechanics in photosynthesis. Where else? What Nature does; science and technology usually try to imitate (hominid see, hominid do).