Ahmed Zewail, 1946-2016


Earlier this month, on Tuesday, August 2, Ahmed H. Zewail, a world renowned Nobel laureate chemist and Caltech’s Linus Pauling Professor of Chemical Physics, died at 70 years of age. As a major figure in the field of chemistry and a personal friend to Linus Pauling, Zewail’s passing is honored and mourned here at Oregon State University.

Zewail was born and raised in Egypt, where he received his bachelor’s and master’s degrees at Alexandria University before going on to attain his PhD at the University of Pennsylvania. After completing his doctorate in 1974, Zewail joined the faculty at the California Institute of Technology, where he remained for the next forty years.

During his tenure at Caltech, Zewail’s team became the first to directly observe the breaking and formation of atomic bonds, also known as transition states. This was initially accomplished in 1987, but the team’s technique had a long way to go before it could be considered revolutionary, to say nothing of routine. Nonetheless, Caltech saw the potential for greatness in Zewail’s work and, in 1990, it named him the first Linus Pauling Professor of Chemical Physics, a newly endowed chair. Upon receiving this accolade, Zewail wrote to Pauling immediately, confiding, “You are one of my personal heroes in science, and I am honored to be holding your chair.” Zewail remained in this position until his passing, frequently stating that it was an honor just to be compared to Linus Pauling, and that he hoped to do justice to that comparison. Important above all else, however, was that Linus Pauling considered him a friend.


Zewail and Pauling at the 90th birthday event, Caltech, February 1991.

Zewail played a major role in revitalizing the relationship between Caltech and Pauling during the 1980s and early 1990s. Pauling had left the Institute in 1963 amidst increasingly strained circumstances surrounding his work for peace and his stance against nuclear testing. From 1986 through 1993, Zewail was in regular contact with Pauling, helping to arrange his visits to the Caltech campus for a variety of lectures dedicated to Pauling’s work and time there. In 1986, Caltech’s eighty-fifth birthday “Salute to Linus Pauling” afforded Zewail the opportunity to present Pauling with a portrait depicting his face on the body of a Pharaoh, captioned “King of Kings of Chemistry.”


“King of Kings in Chemistry”

Later events in which Zewail was involved included Caltech’s first Linus Pauling Lecture in 1989, a second Linus Pauling lecture in 1991, and an additional 1991 symposium on the chemical bond that was held to mark Pauling’s 90th birthday. A year later, Zewail produced an edited volume of the papers presented at this conference, The Chemical Bond: Structure and Dynamics, a work which was the source of much pleasure for Pauling in his final years.

Over time, the two became close friends. Christmas cards were routinely exchanged and Zewail even sent Pauling an announcement on the occasion of the birth of his son. In 1992, Zewail likewise provided Pauling with a manuscript documenting his team’s first successful recording of ultrafast electron diffraction from molecules, a breakthrough that enabled increasingly accurate “pictures” of transition states that had never before been observed by chemists. Pauling responded with praise: this was “a fine piece of work” that would make possible the exploration of previously inaccessible frontiers in the fields of chemistry, physics, and biology.

Zewail won the Nobel Prize for Chemistry in 1999. In continuing to seek out methods to observe transition states, he had pioneered a technique that used laser pulses akin to strobe lights to record the colors of light emitted and absorbed by molecules. This technique was termed “femtosecond spectroscopy.” While chemistry had hitherto inferred specifics of reactions based on the material input and output of a given chemical reaction, Zewail’s work now enabled scientists to see specific changes at the molecular level for the first time.


Crellin and Linus Pauling with Lynne Martinez and Ahmed Zewail, 1991.

To fully appreciate Zewail’s contributions, one must understand that the breaking and shifting of chemical bonds that he worked to observe typically occur in a space of 10-100 femtoseconds, each femtosecond being a millionth of a billionth of a second. Zewail explained the scale of these observations as follows:

Here is the journey in time… 12 or 15 billion years of the Big Bang, and then you come down to our lifespan, which is about 100 years or so – your heart beats in one second. But to go from here [present day] to there [Big Bang] is about 1015, and I am going to take you from the heart into a molecule inside the heart, or eye specifically, and you have to decrease by 15 orders of magnitude to see the beats of this molecule, as you see the beats of your heart. The timescale is fast… if you go from this age of the universe, and you count back from the age of the Earth to the human lifespan to your heart (1 second), and then you go to the microscopic world (sub-second), into how molecules rotate, vibrate, and how the electrons move… In this whole microscopic world here, we reach 10-15 or so seconds, where on the opposite end you reach 1015.

This is the end of time resolution for chemistry and biology, because if you look here, even molecules that are linking undergo collisions on a time scale of 10-14 seconds. A molecule can break a bond and make a bond on this time scale as well. The eye has a molecule called rhodopsin which divides and allows you to see, and that happens in 200 femtoseconds. The way we get photosynthesis to work, and the electron to transfer inside the green plant, is on the order of femtoseconds. So this is the fundamental time scale, and if we were to understand the dynamics of the chemical bond we must understand this time scale.

In other words, the timespan of one heartbeat is to the age of the universe as the timespan of one molecular bond breaking is to the length of an elderly human’s lifespan; the time required by the event is so infinitesimal as to be practically nonexistent. Yet Zewail found that it was at this scale – the “one heartbeat” of a single bond breaking or forming – upon which our entire reality is formed from its molecular foundations up. Zewail showed that events occurring in femtoseconds are the basis for all the occurrences that we take for granted in everyday life.

The ability to observe these events created a new field of study called femtochemistry. And while femtoscopic experiments provide a method for researchers to determine the amounts of energy that hold together different types of chemical bonds, their impact is not limited to chemistry alone. Since the time of Zewail’s breakthroughs in the 1980s and 1990s, many practical applications have emerged from femtoscopic research, including a better understanding of the mechanics of human vision and of the properties of photosynthesis in plants.  Today, most femtosecond lasers are sold not to chemists or physicists, but to hospitals, because of their ability to image very fine tumors. Likewise, in the technology sector, femtosecond pulses can be used to lift material on the micron scale without dissipating heat into a microchip.


In more recent years, Zewail was named Director of the National Science Foundation’s Laboratory for Molecular Sciences, and was nominated by President Barack Obama as both the first United States Science Envoy to the Middle East as well as a member of the President’s Council of Advisors on Science and Technology. In February, Caltech held a symposium titled “Science and Society” to celebrate Zewail’s 70th birthday. At the event, the honoree spoke of his efforts to expand scientific research initiatives in his native country and stressed the importance of holding to a scientific vision. Advocating as he was for education and peace across international borders, Zewail’s message was, without doubt, one that would have made Linus Pauling proud.

On February 28, 2001, on what would have been Linus Pauling’s one-hundredth birthday, Zewail delivered the keynote address at the Linus Pauling Centenary Celebration, a day-long symposium organized and hosted by Oregon State University. In his talk, “Timing in the Invisible,” Zewail reflected on the rapid changes that had arisen in the field of chemistry as a result of breakthroughs in femtoscience. In 1950, when asked what he thought chemists would be studying fifty years on, Pauling responded: “We may hope that the chemists of the year 2000 will have obtained such penetrating knowledge of the forces between atoms and molecules that he will be able to predict the rate of any chemical reaction.” Zewail’s work, in effect, accomplished this ambition. It has given chemists insight into the dynamics of chemical bonding, and thus greater predictive knowledge of the forces and rates of these dynamic changes.

Dr. Ahmed Zewail, who held the Linus Pauling chair at the California Institute of Technology for so long, was indeed the right scientist to carry Pauling’s legacy forward. Now, as that chair sits empty, Zewail is remembered and missed for all that he accomplished as a scientist, as an advocate for social change, and as a friend.

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