Quick Dips

Chemistry in a Different Light

Lasers may be best known for their "death ray" image, courtesy of James Bond movies, but they have more benign and useful purposes, as a team in Auckland University's Chemistry Department are demonstrating. Professor Douglas Russell and his group are using infrared lasers to gain a better understanding of the chemistry of molecular reactions. They're interested in how molecules react when they are heated to high temperatures -- a process known as pyrolysis.

"Simple heating is, of course, one of the oldest known methods of bringing about chemical reaction," says Russell, noting that the subtle changes which take place when food is cooked could be regarded as a form of pyrolysis. Many modern technological developments also depend on pyrolysis reactions. One example is the production of the semiconductor compounds which make up solid-state lasers such as those found in CD players. These components are based on materials such as gallium arsenide (GaAs) or indium phosphide (InP), which can be produced by heating a mixture of gases such as trimethyl gallium and arsine.

"Although this is a well established procedure, there are a number of problems, not least of which is that the gases used are highly toxic," Russell says. He's experienced in this area, having pioneered the use of lasers in the study of semiconductor manufacture at the University of Leicester in the UK, before bringing his work to Auckland.

The Auckland team are studying the detailed chemistry of reactions like this using a high power carbon dioxide infrared laser. With this technique, they hope to learn enough about the chemical pathways involved to point the way to cheaper and safer starting materials and to improve the efficiency of similar processes.

"Lasers have revolutionised many fields of research, especially in atomic and molecular physics, communications, and microsurgery," says Russell. "The use of lasers in chemistry is perhaps less well known, but here too they have had a spectacular impact."

He cites the use of lasers at CalTech in the US to "photograph" molecules in the very act of creation, a process which occurs in the unimaginably short time span of 0.000000000001 seconds.

"Curiously, then, we have come full circle," says Russell. "Chemists are now using lasers to study the processes which are used in the manufacture of lasers."