For more than 150 years, chemists have been dreaming of being able to see atoms moving in real time. They have been imagining reactions occurring and atoms moving in their minds, and now, years later, these mental images are becoming a reality. Using a variety of techniques using extremely short pulses of light or electrons, researchers are now able to see molecules moving in real time.
How It Came to Be
Molecular cinematography has its origins in the 1980s, during which methods designed to capture pictures of molecules appeared. Pump-probe spectroscopy, which was the leading technique at the time, uses a burst of laser light that lasts a few femtoseconds to cause a chemical reaction. Then, a second femtosecond burst appears and “interacts with the molecules in the sample, mid-reaction” (A. H. J. Chem). This causes the light to change its appearance so that a detector can measure it and transform it into a “picture” of the molecule. Researchers can create a flip book of pictures that show all of the stages of a chemical transformation by constantly repeating the experiment while changing the time of the delays between the two bursts. A mode of femtochemistry, this technique sheds light on the specific movements of molecules in chemical reactions in groundbreaking ways.
What It Is
To reveal the structure of their molecules, some researchers use intense bursts of X-rays, while others use scanning tunneling microscopes (STMs). These researchers aim to film events taking place in femtoseconds (fs, 10−15 s) or picoseconds (ps, 10−12 s), with atoms moving mere picometres (hydrogen atoms are approximately 100 pm in diameter). Seeing molecules at this resolution allows researchers to be able to directly observe molecules moving in slow motion for the first time and to observe such motions as electrons moving back and forth, or atomic bonds breaking and vibrating.
The benefits that these new techniques could provide are widespread. They could provide important information that leads to new substances which increase the rate of chemical reactions, artificial models of photosynthesis, or even new ways to control the quantum properties of molecules so that they can be used for communication and quantifying purposes. Similarly, being able to view molecules individually rather than in groups can provide more specific and valuable information about the individual molecules. There are many different ways of being able to see these molecules in motion, and each technique has something unique that it can provide. All of the techniques allow scientists to see how chemistry works up close and in detail.
Mariam Trichas ‘18
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