Ahmed Zewail

(1946-2016) 1999 Nobel Prize in Chemistry | California Institute of Technology, United States

Ahmed Zewail was an Egyptian scientist, known as the "father of femtochemistry". He won the 1999 Nobel Prize in Chemistry for his work on femtochemistry and became the first Egyptian scientist who won Nobel Prize in a scientific field. He was the Linus Pauling Chair Professor Chemistry, Professor of Physics and the director of the Physical Biology Centre for the Ultrafast Science and Technology at the California Institute of Technology.

Obituary

By Bengt Nordén
Chair Professor of Physical Chemistry
Chalmers University of Technology
Gothenburg, Sweden

My Friend Ahmed and I 

Ahmed and I were close – at least that is what I always felt – he called me his big brother (I was one year his senior). While I was more direct about most things, even personal matters, he was generally more difficult to read out and, everybody I know agrees, intrinsically quite private. However, we shared the same sense of humor and the same curious, I would say almost childlike, mindset, when approaching scientific problems – though his was that of a genius.  Ahmed was despite his deeper felt reservation, very social, with an eye for everybody, whether janitor or Nobel laureate. To really see people is something I think I learnt very much from him and indeed find very important in life. His social ability was always combined with humor: I remember many a good laugh together. At the same time he was reflective and a deep philosopher – often finding scholarly parallels with ancient Egyptian or Greek science.

We met more frequently after his Nobel prize, when our families had got to know each other in Stockholm. Actually, the first time we met was only some five years before the prize. Ahmed was touring in Sweden giving seminars at the universities and the story, as Ahmed loved to tell it, goes as follows. My friend, and former colleague from my alma mater university of Lund, then Chair Professor of Inorganic Chemistry at KTH in Stockholm, Ingmar Grenthe, one day called me and suggested I host Ahmed Zewail for a seminar at Chalmers. I should have said “Zewail who?” and Ingmar quite upset asked how I could be ignorant of the most famous laser spectroscopist in the world? My ignorance turned out not to be true though, although I was confused at the moment: as Ahmed and I found out when we met in my office some weeks later, and I pulled the Swedish National Encyclopedia from the shelf, there was a several pages long article about “Physical Chemistry”, authored by myself some 5 years earlier, featuring molecular reaction dynamics studied by fast laser spectroscopy. It contained an illustration from one of Ahmed’s papers! Further, according to Ahmed and Ingmar, I should have said that he (Zewail) would be warmly welcome provided costs for his travel to and stay in Gothenburg were taken care of by Grenthe or the Academy. I translated my encyclopedia article for Ahmed, which initiated our intense discussion about where Physical Chemistry was heading. I would say we found each other then - I even paid his tram ticket when we at sunset went to my home where my surprised wife, Gunnela, improvised dinner for us. Ahmed stayed long that night and many basic questions that we touched upon then and there, we have returned to at our encounters later at Caltech.

After his Nobel prize we got closer, partly because of our joint interest in molecular spectroscopy but partly also, I think, because of a kind of isolation Nobel laureates often feel and me being a member (at the time Chair) of the Nobel Committee. Both of us felt a pressure to behave and not openly admit any of those embarrassing questions and doubts that incessantly plague scientists who want to reach for true understanding of how things really work. We both felt that the Textbook Word and reality are more often than not two different things – a little like a priest who might have his private doubts. Both of us believed in intuition as the best guidance to new theories and experiments, and also allowed ourselves to be secretly skeptical to many “accepted facts” in science.
I used to visit Ahmed at Caltech for a couple of days each November, and one spring I stayed for several months invited as a visiting scholar in his lab. I am very grateful to him (and his wonderful wife Dema) for their ever very generous and amiable hospitality during these stays which were truly inspiring to me. The schedule of the first day of my visits was always that we sat down to discuss various things that had happened in our respective research lives since last time – mostly dominated by Ahmed’s often much more spectacular experimental progress and discoveries. We always started our day with a cappuccino together in the sun outside the campus cafeteria. There he would ask about things related to the Nobel prize, where he, although he was a Foreign Member of the Royal Swedish Academy of Sciences, was often ignorant about who were nominated and so on. (Foreign Members are welcome to those meetings in the Class where nominations and investigations of various candidates are presented and discussed, but have not the right to participate and vote at the general assembly finally deciding on the Nobel prizes and are normally not informed about any details of ongoing investigations, who are hot candidates etc). Ahmed cared very much for the status of the Nobel prize and sometimes had his concerns about true or suspected candidates. This “updating” talk I found the most difficult in our relation as Ahmed’s natural (scientific!) curiosity felt no bounds, while my own integrity and responsibility towards the Nobel institutions prevented me from a completely open information transfer. At the same time these discussions were very useful for me as Ahmed was always an updated source of current development, indications of upcoming breakthroughs, paradigm shifts and so on. Our own fields were thoroughly ventilated, but any development important to Chemistry as a whole was also considered.

Moving from the coffee table to Ahmed’s office, or rather his big conference table and whiteboard across the hallway which we filled with sketches and equations, we plunged into science.  Two topics were recurrent: diffraction of singular electrons in a Young’s double slit setting and coherence of molecular vibrations. I was very much a skeptical Dr Watson, when Ahmed presented new results proudly like a cat putting a dead mouse for my feet. He also enjoyed using me as a Devil’s Advocate: for example, I was generally suspicious to visible oscillations, after having revealed some artifacts in laser spectroscopy back in the 1980-ies, one being a ringing effect due to thermal-lens fluctuations instead of being a real claimed molecular orientation effect due to interaction between the photon field and induced molecular dipole moments, so-called Optical Kerr Effect. Very early his elegant demonstration of recurrent wave-packet travels in the potential diagram of sodium iodide was in focus for our discussions. Was his result maybe in conflict with Heisenberg’s uncertainty principle?  The answer we finally agreed on was, however, “no”, because the fact that Ahmed was exciting all the NaI molecules in phase would make the sample behave differently from a quantum mechanically described single molecule (microscopic system), and be more like a coherently vibrating macroscopic system. 

A pedagogical device, constructed of Perspex and bent steel strings by my engineer Mr Tore Eriksson, and which Ahmed used in his Nobel Lecture illuminated on an overhead projector, showed how a steel ball was moving back and forth in the excited-state potential of Na-I. When the potential curve came close to the ground-state potential, the ball could jump over to the ground state, triggered by a hand-controlled mechanical switch, and then either return to the deep valley representing the bound state of the molecule or move in the opposite direction, corresponding to dissociation into Na and I atoms. Ahmed was very fond of the device which had an honorary position on a shelf in his office. 
Ahmed’s other great interest, in single-electron diffraction, of course, was the embryo to his next big discovery: the use of time-resolved electron microscopy to resolve fast processes. We devoted a lot of time to discuss whether the Coulombic repulsion between the electrons would create a longitudinal “anti-bunching” along the train of electrons, or would just spray the electrons randomly in space. 
As Ahmed’s guest at Caltech I had the privilege and pleasure of meeting his friends at the “Round Table” Wednesday lunches at the Athenaeum, 10 of Caltech’s most outstanding scientists, including Rudy Marcus and Jack Roberts, the latter who passed away in October 2016, at 98, was the legendary inventor of physical organic chemistry and the modern use of NMR for studying molecular structure and dynamics.  To a newcomer these lunches were indeed inspiring and also a little scary – I had suddenly to stand up for all science, politics and economy that had been going on in Europe since my last visit; generally I managed to duck for the kill questions although not always. At these Round Table discussions about all and everything, I also realized how Ahmed was the born survivor – a fish in his right element – the same way as he survived when he was first up for interview at Caltech and became afraid he would misspell Feynman when writing his name on the blackboard – he got away with it by – after writing Fe… turning around with a charming smile saying: we all know how to spell Feynman do we not? Whereupon everyone laughed.

To Ahmed Zewail the coming generation of young scientists was very important – and Egypt youth had a special place in his heart – as will Egypt be for ever grateful to Ahmed Zewail for all his influence and academic initiatives there – such as the Zewail City of Science and Technology – his lifelong dream, inaugurated with Ahmed as its Chair in 2011. He also played a seminal role for the early development and establishment of the Molecular Frontiers Foundation, being Chair of its first Scientific Advisory Board and himself being speaker at many of its symposia, explaining results from the research frontiers in his characteristic vivid, simplistic and pedagogical way.  Molecular Frontiers owes Ahmed a lot in that he created the discussion atmosphere that today is a hallmark of the organization: the youth are prized for their questions, not for knowing the answers!

My first experience of this talent of his was at a Lindau Nobel Laureate Meeting where I was asked to moderate a round-table discussion, an occasion that gave rise to another humoristic anecdote that Ahmed liked to refer to. The Nobel laureates around the table, in addition to Ahmed were Harry Kroto, Paul Crutzen, Richard Ernst and George Olah (see Figure 1). I received scraps of paper with questions from the floor – mostly young PhD students who had received stipends to partake in the meeting. As most questions were thoughtful and scientifically advanced (read boring), I smuggled myself in a few that fired up the discussion considerably: referring to Alfred Nobel, one asked how dynamite really works? What is the role of the stabilizing agent (a dispersion of dry diatom silica organisms or simply sawdust)?  A lively discussion started among the Nobel laureates with speculations all over the place, one was about acoustic damping, until suddenly a shout from the audience interrupted - Nobel laureate Manfred Eigen rose and claimed we were all wrong, and the true explanation how the tricky nitroglycerine was tamed was due to that the stabilizer reacts with radicals, quenching chain reactions.  

We were interviewed afterwards by the Editor of Chemical & Engineering News, Dr Madeleine Jacobs, who, when she introduced herself, turned to me: “we have actually met before but maybe you don’t recognize me with clothes on”.  This comment which led to great general amusement, not least Ahmed’s, had an explanation in that both of us had started our days with a swim workout in the hotel pool before breakfast.  After a couple of days we greeted each other at a distance, being the only ones in the large pool but I had obviously not recognized her when she reappeared in the conference without swim cap and “with clothes on”.  Another amusing incidence occurred when I was going to check out from the hotel and had no cash (they refused to take any cards). Behind me in the line was Dr Lorie Karnath, restless as she had to catch a flight, and possibly also feeling pity for me: she bailed me out and paid my room and thus probably rescued me from an embarrassing fate. In return I later treated her to a nice meal and great wine at the Grand Hotel in Stockholm. Together with Prof Magdalena Eriksson she later became instrumental during the first stumbling, founding steps of creating Molecular Frontiers Foundation; both of them are still highly active in the core of the MFF organization.

A special memory I have with Ahmed was one summer afternoon when he was on his way from Lund to a spectroscopy conference in Copenhagen, and made a detour via our summerhouse at a little fishing village by the Sound between Sweden and Denmark. He stayed for an early dinner but as he was going to call for a taxi to take him to the hydrofoil ferry in Malmö, I suggested: why don’t we sail you over and you save some money?  Soon we were under sail with my neighbor and very close friend, orthopedic professor Björn Persson, in his boat with course straight west. The wind was not cold, but brisk and we sailed fast. After a little more than two hours we entered the mouth of the harbor of Copenhagen, reduced sail and moved slowly into the very heart of the continental city. Both Ahmed and I remembered the event fondly, this was the first time for him in a sailing yacht – his only experience of small boats being from the Nile when he was a boy. He enjoyed every moment, especially the magic feeling when we were silently approaching the big city in darkness with its many lights ashore. We landed in Christianshavn, a part of Copenhagen which is a little like Venice with narrow channels and many small restaurants. It was close to midnight and we wondered if it would be possible to get anything to eat before Ahmed had to depart for his hotel and we return to Sweden. Close to where we had docked the boat, we found a small pub in the basement which was closing with the last patrons just leaving. When Ahmed asked the owner whether we could have something very simple to eat, he was most reluctant, but Ahmed’s charm quickly broke down any resistance, and soon we found ourselves sitting together with him and the kitchen staff having a veritable feast meal – one of the waiters (a Portuguese) brought his guitar and began to entertain us all with emotional Fado songs. 

The last time I saw Ahmed was when Gunnela and I visited Pasadena in November 2015. I gave a seminar in his group on our recent discovery of a new elongated conformation of double-stranded DNA (the “sigma form”) and its potential biological role and why any form of organic life can only exist in a water-rich environment. He had many good points and also suggested a clever mechanistic complement to my explanation of the inhomogeneous conformational reorganization that we call “disproportionation”. Earlier the same day he had shown me some amazing results from time-resolved single-electron microscopy, visualizing in real time the coherent travel of phonons along a set of hydrocarbon chains aligned at a surface. At the end of the chain the wave was reflected and returned back. As he commented when I interrupted him to guess that result: “you saw it in a femtosecond, didn’t you?”

The last photo I have of Ahmed (and myself) is from my 70th birthday symposium in Gothenburg in early May 2015. As usual he gave a captivating talk (watch the video here), appreciated as much by the professional scientific audience (many Nobel Laureates) as by the more than 200 high-school students.  

Ahmed, I am most grateful to you for all inspiration you gave me over the years and for your deep-felt friendship, the memory of which I will carry in my heart as long as I live.  

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