Images of Molecule Movement Taken in a Billionth of a Second

Investigators have devised a way to take very rapid snapshots of molecular and atomic movement, thought to be a major advance in surface science, the study of chemical reactions taking place on the surface of solids.

A study details how carbon monoxide molecules move on a copper substrate when bombarded with very fast laser pulses--a femtosecond is one millionth of a nanosecond--and these laser pulses track their movements. The study was published in the July 30, 2004, issue of the journal Science.

"It was possible to identify the individual site-to-site displacements of molecules undergoing ultra-fast dynamics induced by femtosecond laser pulses,” said Dr. Ludwig Bartels, an assistant professor of chemistry at the University of California, Riverside (UCR; CA, USA), describing the method as a way of getting something similar to snapshots of the molecules' movements. Other investigators of the study were from Columbia University (New York, NY, USA), and Rowan University (Glassboro, NJ, USA).

"Scanning probe microscopy has the capability of reaching directly down to the natural spatial scale of atoms and molecules,” said Dr. Bartels. "While femtosecond laser techniques have the capability of reaching down to the time scale of atomic events, there has been considerable interest in the very challenging problem of combining these two capabilities. While we have not yet achieved the ultimate goal of a real-time, real-space movie, the current paper reports what we believe to be a very significant advance in combining the two very powerful techniques.”

The new method allows researchers to explore the essential questions in surface science, according to Dr. Bartels and coworkers. They include questions such as: what substrate excitations drive surface diffusion of absorbates? Surface diffusion is a very fundamental and significant process in surface science, playing a major role in processes as varied as crystal formation and catalyst activity.

"This is very basic research but it has implications for many other areas in science. Catalysts, like the one in the exhaust system in every car, are made from a porous material. The exhaust gas is passed through it and the pollutants such as carbon monoxide and nitric oxide can stick to the surface of the catalyst material,” remarked Dr. Bartels.

A small segment of the catalyst surface can convert the pollutant into benign gases while the rest of the surface supports these active areas. Comprehending how carbon monoxide travels across a catalyst surface to find the active areas may eventually allow the creation of more efficient catalysts. The study's results offer a new method of studying the extremely rapid movement of carbon monoxide on surfaces.




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