Personal and Scientific Reminiscences

Majed Chergui, Rudolph A Marcus;John Meurig Thomas;Dongping Zhong;

• Publisher: WSPC (EUROPE)
• Year: 2017
• eBook ISBN: 9781786344373
• Topic: Physical Sciences
• Subtopic: Science History

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A compilation of wonderful tributes to the late Ahmed Zewail (1946-2016), considered the 'Father of Femtochemistry', a long-standing icon in the field of physical chemistry, and the father of ultrafast electron-based methods. The book contains testimonies by friends and relatives of Zewail and by outstanding scientists from around the world who worked or have been affiliated with the Nobel prizewinning professor. Each contribution describes the author's own unique experience and personal relationship with Zewail, and includes details of his scientific achievements and the stories around them. Personal and Scientific Reminiscences collects accounts from the most important individuals in the physical and chemical sciences to give us a unique insight into the world and work of one of the great scientists of our time.

--> Contents:

• Ahmed Zewail: Ultra Scientist and Citizen (Dudley Herschbach)
• Ahmed Zewail: Larger than Life (Roger Kornberg)
• Stories from the Round Table (Marshall Cohen, Charlie Campbell and Rudolph A Marcus)
• Ahmed Zewail: Great Scientist, Dear Friend (Harry B Gray)
• In Memory: Ahmed Zewail (Jack Dunitz)
• Some Personal Recollections of Ahmed Zewail (Fred C Anson)
• My Friend Ahmed and I (Bengt Nordén)
• A Tribute to Ahmed H Zewail (David C Clary)
• Ahmed Zewail — A Great Scientist and Inspiring Friend (Amyand David Buckingham)
• The Pyramid Builder (Majed Chergui)
• A Remembrance of Ahmed Zewail (Chad A Mirkin)
• 4D Electron Tomography: Some Recollections of the Summer of 2000 (Wolfgang Baumeister and Juergen Plitzko)
• Anatomy of a Friendship and Collaboration (John Meurig Thomas)
• Ahmed the Explorer (Martin Pope)
• Ahmed Zewail: Advancing Chemistry (Norbert D Dittrich)
• Four Decades in the Sub-basement — Walks of Life with Ahmed Zewail (Spencer Baskin)
• Ahmed Zewail: An Honor to Egypt and Fellow Countrymen (Jehane Ragai)
• Timing with Light (Archie Howie)
• Ahmed Zewail — A Towering Visionary (Collin Humphreys)
• A Glimpse of the Evolution of Adiabaticity (Noel S Hush)
• Ahmed Zewail: Science and Scientist (Joshua Jortner)
• Brief Encounters with Ahmed Zewail (Malcolm Longair)
• "Peter: You Have Taught Me that Electrons are Blue!" (Peter Edwards)
• How I Lost My Funding to Zewail (Shaul Mukamel)
• The Brilliance of Ahmed Zewail (Paul Midgley)
• Ahmed H Zewail: Remembering a Hero and Friend in Science (Jörn Manz)
• Ahmed Zewail: A Reminiscence (Paul E Dimotakis)
• "Stop All the Clocks" (Dmitry Shorokhov)
• My Time with a Giant (Dongping Zhong)
• Ahmed Zewail — An Inspired and Inspirational Scientist and Man (David Phillips)
• My Memories of Ahmed Zewail — From a Snowy Northern Sweden to the Nobel Prize (Villy Sundström)
• The Physical Basis of the Amyloid Phenomenon (Christopher M Dobson)
• High-Intensity Mentoring and Excitement from Ahmed Zewail (Marcos Dantus)
• BCH-codes are (In Fact) Good! (Michael J Collins)
• Ahmed Zewail: A Reminiscence (Ahmed Okasha)
• Goodbye My Love (Dema Faham)

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--> Readership: Students, practitioners and researchers of chemistry, physical chemistry and physics interested in learning about one of the great minds in physical chemistry. -->
Ahmed Zewail;Memorial;Physical Chemistry;Femtochemistry;Nobel Prize0

Chapter 1

Ahmed Zewail: Ultra-Scientist and Citizen

Dudley Herschbach*

To my regret, I met Ahmed Zewail in person only a few times. We first met in Spring 1976, when he arrived at Caltech, newly appointed as an assistant professor. I was visiting that semester, on sabbatical leave from Harvard. Ahmed impressed me as very bright, cheerful, and witty, brimming with ideas and zest. About a decade later, although we had not met again, I was intrigued by his innovative papers. Particularly instructive was his exposition of the role of coherence in laser spectroscopy.¹ Moreover, using molecular beams and ultrafast lasers, Ahmed had developed a pump-probe technique that mapped, in “real time,” trajectories of products from photoinduced reactions,² exemplified by hν + ICN → I + CN. At first, the method was limited to such unimolecular reactions, initiated by photodissociation. Bimolecular reactions seemed inaccessible because means were lacking to define a time zero.

That limitation was soon overcome, as I learned at a workshop held at Jerusalem in November 1986, devoted to stereochemical aspects of chemical dynamics.³ Ahmed was not there, but Dick Bernstein had become a devoted apostle. A leading pioneer in molecular beam studies of chemical dynamics, Dick had, some years before, moved to the University of California at Los Angeles. Gleefully, he said he was “now a post-doc with Ahmed.” In that collaboration, Dick made a key contribution by advocating a technique then recently developed by Curt Wittig at the University of Southern California.⁴ It exploited the inherent mutual orientation of molecules in a weakly linked van der Waals adduct. The prototype case formed an XH … OCO adduct in a supersonic molecular beam. Then ­photolysis of the hydrogen halide initiated the bimolecular reaction, H + OCO → OH + CO, propelling the H atom into the nearby carbon dioxide. The collision was roughly collinear by virtue of the precursor geometry. Zewail’s team at Caltech used a picosecond laser pulse to ­photodissocate the HX, followed by a delayed picosecond laser probe of the OH product.⁵ Thereby, they were able to clock the formation and decay of the HOCO reaction complex. The key feature was that the first pulse established the zero of time for the bimolecular reaction, enabling a series of probe pulses to record the “real-time” evolution of the correlated products.

Soon Ahmed was able to make use of femtosecond lasers, initiated by Chuck Shank and colleagues at Bell Labs. That greatly enhanced the time resolution, launching the awesome saga of femtochemistry. The name was suggested by Dick Bernstein; he and Ahmed published in 1988 a fine overview of the evolution and prospects of femtochemistry.⁶ Ahmed baptized his prolific labs FEMTOLAND I, II, III and joyfully spoke of his “Femtosecond Dream” and “Femtocopia.” The overview sparkled with evangelical fervor, concluding with: “This happy marriage of ultrafast lasers and chemistry promises an exciting future for this field of real-time molecular reaction dynamics.”

As part of its centennial year, Caltech held a three-day symposium to celebrate Linus Pauling’s 90^th birthday on February 28, 1991. A year before, Ahmed had been appointed to the newly endowed Linus Pauling Professorship for Chemical Physics. On that occasion, he mentioned with a smile that two days before he had become half as old as Pauling. Aptly, the symposium extolled both Linus and Ahmed. The lectures became a book, The Chemical Bond: Structure and Dynamics, edited by Ahmed.⁷ In his preface, he proclaimed that “as X-rays introduced the distance scale for molecular structure,” now the advent of femtochemistry has ­“introduced the time scale for the dynamics of the chemical act itself — the transition states between reagents and products.” Five chapters commemorated structure, two of them from lectures by Pauling, and the others by Alex Rich, Max Perutz, and Francis Crick. Four chapters dealt with dynamics: three from lectures by George Porter, John Polanyi, and me. The fourth chapter, not presented as a lecture, was the sparkling evangelical overview that Ahmed had published with Dick Bernstein,⁶ brought up to date. Dick had died in 1990; that chapter abides among his definitive legacy to chemical dynamics.⁸

Like many physical chemists of my vintage, I am among the many scientific grandchildren of Pauling. My Ph.D. mentor was one of his most distinguished scientific sons, E. Bright Wilson. I was particularly glad to take part in the Pauling symposium because, 33 years earlier, I first visited Caltech at the behest of Linus, when he was Chairman of the Chemistry Department. Back then I gave, for the first time, a talk about my fledgling plans and hopes for molecular beam studies of chemical reaction dynamics. My lecture at the Paulingfest sampled what grew out of those plans. Particularly, I emphasized how the role of electronegativity — a favorite theme of Linus — nicely explains some striking aspects of elementary reactions. Ahmed protested that I had made it too simplistic. Perhaps so, yet it seemed to capture the essence, emulating Linus. I pointed to a photo, shown here as Figure 1.1, which graced the dust jacket of The Chemical Bond book. It surely exemplified, in a simplistic way, his favorite concept of coherence!

A few months later, Linus, Ahmed, and I met again, to celebrate the award of the Pauling Medal to Rudolph A. Marcus. Ahmed gave a talk on the Br + I₂ reaction, which proceeds via a “sticky” collision complex.⁹ His new FEMTOLAND II apparatus made it possible to determine the lifetime of the complex to be ∼50 ps. My talk, apropos of the 1991 presidential election campaign, was titled “How do electrons choose between candidate reaction products?” I passed out a ballot listing two candidates for each of the eight reactions. Molecular beam experiments had confirmed the predominant products, mostly “winners by a landslide.” But few of the voters chose more than 3/8 of the winners, although nearly all had Ph.D.s in chemistry. To my dismay, Ahmed and Rudolph each got only 2/8! Choices made on the basis of energetic or statistical considerations proved misleading. Again, Pauling-like heuristic reasoning predicted the winners, by simply taking account molecular orbital asymmetry arising from differences in electronegativity. Afterward, Ahmed sent me a brief letter, saying ­(diplomatically?) that his students “didn’t like molecular orbitals.”

Figure 1.1. Linus Pauling and Ahmed Zewail strolling on the Caltech campus with ­coherent strides.

In November 1992, Ahmed visited Cambridge to deliver a joint Harvard–MIT physical chemistry seminar. As well as giving a scintillating talk on femtochemistry, he romped through visits with faculty, students, and postdocs, the day at Harvard before his talk and at MIT the day after. I had the opportunity to engage in a wide-ranging discussion with him for two hours in the morning and another four hours during and after dinner. Throughout, Ahmed was delightfully vivacious, both in describing his work and asking many searching questions. He was especially curious about a whimsical verse I had hung up near my desk (see Figure 1.2). I had composed it after a seminar given at Harvard in the early 1980s by Geraldine Kenney-Wallace. At Toronto, in 1974, she had set up an ultrafast laser that enabled her to elucidate the formation of solvated electrons. Back then, “ultrafast” meant picosecond. The format of my verse mimics that in a booklet of poems by Robert Williams Wood (1868–1955) titled How to Tell the Birds from the Flowers (1917). Wood was an outstanding physicist, celebrated for his work on spectroscopy, physical optics, infrared and ultraviolet photography, ultrasonics — and for his humorous enterprises. I had composed several poems using Wood’s format, which required coming up with two sketches with titles that are similar in looks and sound. Despite some effort, I had failed to concoct anything tractable for femtochemistry. Ahmed was gracious in accepting my apology. In turn, I noted that the words of the poem would apply to his femtochemistry, if the final line were changed to read: “They dance faster but cannot elude our throbbing lights.”

Figure 1.2. Verse inspired by solvated electrons tickled by a pulsed laser.

At dinner, among things prompted by Ahmed’s seminar, there came up a question about a quote he had shown on his last transparency slides (no PowerPoints yet!): “What good is a newborn baby?” It was attributed to Michael Faraday, responding to the query: “What will it be good for?” which greeted his discoveries in electromagnetism. As I was a life member of Friends of Benjamin Franklin (akin to Baker Street Regulars for Sherlock Holmes), I mentioned that the newborn baby response was made by Franklin in 1783, after observing in Paris the first flight of a hot-air balloon. The following week, Ahmed sent a letter asking for more information about the newborn baby quote. I obliged by sending copies of two scholarly articles by historians who had explored the question.¹⁰ I mention this minor episode because of Ahmed’s avid interest. Years later, he evidently had made a very thorough study of Franklin. Ahmed gave a splendid talk, “Franklin’s Vision,” at the Tercentenary celebration of Franklin’s birth held in 2006 at the American Philosophical Society in Philadelphia.¹¹ In his office, Ahmed had Franklin’s bust, “as a daily reminder of what it means to be a scientist in service of society and a citizen of the world at large.”

Shortly after his visit, Ahmed sent a preprint of a theoretical paper, treating femtosecond dynamics on model potentials.¹² It mapped out the motion of a wave packet and its dispersion on repulsive, attractive, and barrier-crossing potentials, obtaining estimates of reaction times and relating them to parameters of the dynamics. A key issue was the time scale over which wave packets remain coherent or localized. The analysis, replete with well-designed diagrams and easy-to-follow equations, demonstrated that, on the time scale of femtoseconds to picoseconds, the wave packet spreading is relatively insignificant. This paper, a contribution to a Festschrift celebrating my 60^th birthday, included a fulsome dedication, concluding: “We wish him the best and expect the Herschbachian contributions to continue with every femtosecond full of joy!” My reply noted that 60 years contains 3 moles of femtoseconds.

In February 1993, I visited Caltech again to give the Pauling Lecture, hosted by Ahmed. On my arrival, he graciously thanked me for the congratulatory message I had sent him on the announcement of his Wolf Prize win. Then, laughing about the 1991 ballot, he brought up the role of molecular orbitals and electronegativity. He even praised the exposition of it in my chapter in The Chemical Bond book.⁷ Also, he had evoked a frontier molecular orbital in discussing the Br + I₂ reaction.¹³ I had brought along the ballot. His colleague, Jack Roberts, had heard about it and asked to vote; he scored 6/8. Ahmed’s secretary, who never studied a chemistry course, also voted and scored 4/8, pleased that her score equaled the sum of Ahmed and Rudolph.

As well as discussing current experiments in our labs, Ahmed was eager to hear stories about Linus, especially some told to me by Bright Wilson.¹⁴ Ahmed, like me, had found the 1935 text by Pauling and Wilson, Introduction to Quantum Mechanics, unexcelled as an introduction (still in print!). Bright, as his Teaching Fellow, took notes on Pauling’s lectures. Bright recalled that Linus, when responding to a question, would often pretend that he had not considered it before. He would work out the mathematical solution on the blackboard, step-by-step, with commentary implying it was a fresh excursion. Bright knew that Linus had carefully prepared the derivation before class. Bright also told me that, although he did not remember which of them had written various parts of the book, those written by Linus were turned out at a steady pace, without any revision. Several of Ahmed’s co-authors on papers have testified that he too, in writing as in speaking, was remarkably adept and fluent.

Dinner the evening before my lecture was the last occasion during which I saw Linus. He told a story Ahmed enjoyed and had not heard before. Linus said that one day, just 15 minutes before his class, the phone rang. It was Ava Helen, his wife, so...

Table of contents

• Cover Page
• Title
• Copyright
• Preface
• List of Contributors
• Contents
• Chapter 1: Ahmed Zewail: Ultra-Scientist and Citizen
• Chapter 2: Ahmed Zewail: Larger than Life
• Chapter 3: Stories from the Round Table
• Chapter 4: Ahmed Zewail: Great Scientist, Dear Friend
• Chapter 5: In Memory: Ahmed Zewail
• Chapter 6: Some Personal Recollections of Ahmed Zewail
• Chapter 7: My Friend Ahmed and I
• Chapter 8: A Tribute to Ahmed H. Zewail
• Chapter 9: Ahmed Zewail — A Great Scientist and Inspiring Friend
• Chapter 10: The Pyramid Builder
• Chapter 11: A Remembrance of Ahmed Zewail
• Chapter 12: 4D Electron Tomography: Some Recollections of the Summer of 2000
• Chapter 13: Anatomy of a Friendship and Collaboration
• Chapter 14: Ahmed the Explorer
• Chapter 15: Ahmed Zewail: Advancing Chemistry
• Chapter 16: Four Decades in the Sub-basement — Walks of Life with Ahmed Zewail
• Chapter 17: Ahmed Zewail: An Honor to Egypt and Fellow Countrymen
• Chapter 18: Timing with Light
• Chapter 19: Ahmed Zewail — A Towering Visionary
• Chapter 20: A Glimpse of the Evolution of Adiabaticity
• Chapter 21: Ahmed Zewail: Science and Scientist
• Chapter 22: Brief Encounters with Ahmed Zewail
• Chapter 23: “Peter: You Have Taught Me that Electrons are Blue!”
• Chapter 24: How I Lost My Funding to Zewail
• Chapter 25: The Brilliance of Ahmed Zewail
• Chapter 26: Ahmed H. Zewail: Remembering a Hero and Friend in Science
• Chapter 27: Ahmed Zewail: A Reminiscence
• Chapter 28: “Stop All the Clocks”
• Chapter 29: My Time with a Giant
• Chapter 30: Ahmed Zewail — An Inspired and Inspirational Scientist and Man
• Chapter 31: My Memories of Ahmed Zewail — From a Snowy Northern Sweden to the Nobel Prize
• Chapter 32: The Physical Basis of the Amyloid Phenomenon
• Chapter 33: High-Intensity Mentoring and Excitement from Ahmed Zewail
• Chapter 34: BCH-codes are (In Fact) Good!
• Chapter 35: Ahmed Zewail: A Reminiscence
• Chapter 36: Goodbye My Love
• Additional List of Obituaries