Stanford University | Stanford, California
For fundamental studies of the dynamics of chemical reactions, including the development of techniques to observe molecules as they react.
It is one thing to know how to initiate a desired chemical reaction, but quite another to control it, and still another to actually understand precisely what's going on with the reaction at its fundamental levels. The traditional technique for such purposes has been spectroscopy of various types, such as using light at various wavelengths to generate spectra that reveal the composition of materials, or mass spectrometry that identifies materials by differences in atomic mass. Still, while these tools can identify, define, and analyze, they lack the ability to influence or control what happens in chemical reactions at a precise level. Richard Zare's development of laser-induced fluorescence (LIF) allowed us to do this for the first time. The technique can not only detect and identify molecules, but also trap and manipulate them at the quantum level in unprecedented ways.
LIF uses laser light of a fixed wavelength (color) to cause atoms or molecules to fluoresce, exciting them to a specific higher energy level and then studying the light emitted at different wavelengths when they relax to various ground-state levels. Zare was still only an undergraduate at Harvard, pursuing a double major in chemistry and physics, when the invention of the laser was announced by Ted Maiman of Hughes Research Laboratories in 1960. After obtaining his Ph.D. and taking a faculty position at MIT, and then at the University of Colorado at Boulder, he first conceived of the idea of inducing fluorescence through a laser, and set out to investigate the concept, building a helium-neon laser and conducting experiments on the potassium dimer molecule K2. The results revealed previously unobserved vibrational and rotational molecular levels of the molecule, demonstrating the practicality and usefulness of the LIF technique.
Zare expanded and extended his LIF work into further areas, including the analysis of liquid samples, opening its use beyond physical chemistry into important biological and medical applications including DNA sequencing. Such wide-ranging applications highlight the many advantages that laser-induced fluorescence offers over other techniques. Because a laser can be precisely tuned to different wavelengths and even sweep through them, various electronic, vibrational, and rotational states can be accessed and studied with great precision and sensitivity on very fine timescales, not just in the relatively sedate setting of a lab bench but under extreme conditions such as inside flames or electrical arcs and sparks. It is such capabilities that make LIF such a powerful means of investigating and analyzing so many types of reactions, even down to the level of single molecule interactions.
Zare has also turned his attention to another important frontier of physical chemistry, the study of microdroplet reactions. He demonstrated that many types of reactions are greatly accelerated and facilitated through the interactions of microdroplets at liquid surfaces rather than in bulk liquids, caused in part by strong electric fields at droplet surfaces, as revealed in LIF imaging.
One could wax on highlighting the fundamental discoveries created by Zare’s technical innovations beyond LIF. But it is useful to highlight recent work deriving from his long-standing interest in analytical methods. This started in earnest with his development of “two-step” mass spectrometry, a method in which neutral molecules are photoevaporated from a surface and then ionized in a second step to catch only the most fragile and interesting molecules. This analytical work really took off, and merged with fundamental chemistry, when he exploited “ambient ionization,” a method introduced by Nobelist John Fenn. Zare expanded on this theme to capture molecules that were short lived and those that play a role in breaking chemical bonds.
Presently a professor of chemistry and physics at Stanford University, Zare previously taught and trained many students at MIT, the University of Colorado, and Columbia University. He is an unquestioned international leader in both fields and is the recipient of multiple honors and awards, among them the Priestley Medal of the American Chemical Society and the Irving Langmuir Prize of the American Physical Society, all testifying to his vital contributions in both disciplines. In addition to membership in the National Academy of Sciences and the American Academy of Arts and Sciences, he has been elected to an elite selection of international academies, including the Royal Society (United Kingdom), the Indian Academy of Sciences, the Chinese Academy of Sciences, and the Swedish Royal Academy of Engineering Sciences.
When it was first introduced to the world, the laser was dismissed by some as little more than an interesting curiosity, a "solution in search of a problem." Richard Zare has shown that the laser can be used to solve a myriad of problems and answer a multitude of scientific questions, particularly when those problems and questions are addressed by a scientist with the insight and creativity he has demonstrated throughout his career.
Information as of March 2023