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# How to take a molecule’s temperature

Although they can't stick the thermometer any of the usual places, researchers have found a way to take the temperature of a single molecule. How? A ray of light.

Heat is a simple concept and a different measurement. When we measure heat, we measure a particular part of an object's energy. Specifically we measure the average vibrational energy of its component atoms. The more energy is pumped into the object, the faster its various little pieces start wiggling around. The more they jiggle, the hotter the substance is. (It's this uncontrolled motion that causes damage to us, as this fast motion destroys the proteins and other complex molecules that make the human body.)

It seems like the fewer atoms there are in a structure, the easier it should be to take its temperature. Fewer bits; less moving molecules whose speeds need to be averaged out. That's not the case. In most cases, we're not measuring speed, we're measuring volume. When we stick a thermometer in something, the object's heat radiates into the bulb of the thermometer. The mercury atoms in the bulb of the thermometer speed up, and in their fast-moving state, push against each other. This causes the mercury to expand, pushing a thin jet of liquid up the thermometer that we read as, say, 98.6 degrees.

A single molecule isn't large enough to be measured this way. It isn't even big enough for scientists to measure its expanded motion directly. As technology shrinks down, measuring the temperature change of extremely small objects has become more important, but there hasn't been a way to do it. Until now.

Scientists at Rice University have found a way to test the temperature of a single molecule at a time. The molecule is suspended between two gold wires. To take the temperature of the molecule, the scientists use Raman scattering. Certain wavelengths of light are sent towards the molecules. When they come back, their energy has changed. That change is due to the temperature of the molecule. When a molecule is chilled, it warms itself in the light, and the light that comes back is slightly less energetic than it had been when it went in. As the molecules warms and has more energy, the light that's sent in sometimes gets an extra kick of energy on its way out.

By measuring the difference in the energy of light before and after it interacts with the molecule, scientists are able to determine the molecule's temperature. This could help pave the way for practical breakthroughs in nanotechnology. According to Douglas Natelson, the leader of the experimental team, it's the first practical research into heating and cooling on a nano scale:

"In general, you can't do it. There's a lot of modeling, but in terms of experimental things you can actually measure that tell you what's happening, everything is very indirect. This is an exception. This is special. You can see what's happening."