DAVID ARNOLD WILLIAMS T.W. HARTQUIST Department of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, U.K.
David Williams was Perren Professor of Astronomy at University College London for eight years, and became Emeritus Perren Professor on 1 October 2002. His establishment of the UCL Centre for Cosmic Chemistry and Physics, and his motivation of experimental and theoretical physicists and chemists to investigate fundamental processes of importance in astronomy are among the numerous accomplishments that he has achieved since moving to London. David was born on 9 September 1937, in Nottingham. His father, James Arnold Williams, was a Unitarian minister, then serving the High Pavement Chapel in that city. Arnold Williams had trained for the ministry at Queen’s University Belfast and at the University of Manchester, and in the latter city met Frances Barbara Begg, who became his wife and David’s mother. Barbara had obtained a BSc from the University of Manchester in mathematics and physics, and the household she created with Arnold Williams had an academic atmosphere. It amused David that, in later life, he was able to use his mother’s books on dynamics and calculus when he himself was a student, and again when teaching. The Williams family moved to Northern Ireland in 1945, where Arnold Williams ministered to a congregation in Larne. David was educated at Larne Grammar School, and also through reading widely in the large library that accumulated in the Williams household. David’s parents and his school gave strong encouragement to his interests in science, though David’s enthusiasms were dominated for a long while by playing rugby and by music. David entered the Queen’s University of Belfast in 1956 to study physics, chemistry, and pure and applied mathematics. He received lectures from the eminent scientists Alexander Dalgarno and David Bates, both of whom were to influence significantly his later career. He took a degree in physics after three years, and an honours degree in applied mathematics a year later. During this time, David met Doreen Jane Bell, then a medical student. Jane was president of the Women’s Student Union while David headed the men’s Student Union, and they met while representing their Unions at various dinners, to discover that – unknown to each other – they had shared the same physics lectures in their first years. They soon found and shared many other more important common interests, and married in 1964, after Jane had completed her medical studies and David had graduated with his PhD. They remain happily married today.
Astrophysics and Space Science 285: 613–617, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands.
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It was inevitable that David would try to register for research in the Department of Applied Mathematics at Queen’s, given the very high reputation of that Department. Alex Dalgarno was his supervisor, on a project concerned with the properties of molecular hydrogen, a species suspected to exist in space but not then detected. This project opened David’s eyes to the excitement of astrophysics, and the opportunities of unbridled speculation. When Alex left to spend a year in the USA, David Bates became David’s supervisor, on a project investigating the collisions of protons with hydrogen. This work involved the first use of molecular basis functions in the treatment of atom-atom scattering. After his PhD research was completed, David moved to the Manchester College of Science and Technology (later to become UMIST) where he began his academic career as an Assistant Lecturer. He realised that he didn’t wish to continue with atomic collisions research, and wanted to move into astrophysics. Following Alex Dalgarno’s advice, he began to think about molecules in space, and was able to take up a position at the NASA Goddard Space Flight Center to work with Ted Stecher. Ted had just discovered the extinction ‘bump’ in the ultraviolet, so Ted and David began to think about dust and molecule formation, and in 1967 published their famous paper on the photodissociation of the hydrogen molecule. By then sure that the area of molecular astrophysics was where he wished to work, David returned to the UK, and to a new job in the new institution, UMIST. The unfolding field of molecular astrophysics was an exciting one, and David was lucky enough to enter it at an early stage. Some of his work in the late 1960s and 1970s concerned physical processes on interstellar dust, including adsorption, desorption, and sputtering. He addressed the mechanisms by which many of the first detected molecules, such as OH, CH, CH+ , and H2 CO, are formed and excited. He co-authored a paper on H3 + , well before that molecule figured prominently in the chemical network proposed by Herbst and Klemperer. David and his first postgraduate student, Tom Millar, co-authored their first papers in 1975. One of these addressed the formation of large interstellar molecules through radiative association, a process still considered viable. Others also concerned gas phase chemical networks. David also discussed the possible contribution of surface reactions to interstellar chemistry, and this is an area that has interested him ever since. Papers on surface chemistry with his students Tom Millar, Michael Leitch-Devlin, and John Pickles appeared in the mid-1970s, and contrasted with the works of others who focused entirely on gas-phase schemes. In 1978 David published his first paper with Walt Duley, and thus began a long and fruitful collaboration which has contributed to our understanding of the nature and roles of interstellar dust. Alumni of the UMIST group, such as Tom Millar and Ant Jones, were key players in this extended programme. I first met David in 1981, when he asked a question at the end of a seminar I gave in Manchester. Not knowing the identity of the questioner, I proceeded to argue with him about the details of the Stecher-Williams process for the excitation and dissociation of interstellar molecular hydrogen. Needless to say, I was wrong.
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Our friendship began at this point but really opened up in 1982 at a meeting in Toledo, Spain. On the flight back, our conversation triggered the development of a long collaboration and the great affection and respect that I have for him. Our first of roughly forty joint papers (to date) appeared in 1984, and concerned the interrelation of chemistry and dynamics in star-forming regions. Early in that collaboration I learned that David was interested not so much in explaining measured abundances of interstellar species as in what those explanations might reveal about the evolution of the astronomical objects in which the molecules exist. John Dyson played an active role in my collaboration with David throughout the 1980s, and the three of us have published together as recently as 1998. The arrival of Jonathan Rawlings as a postgraduate student (and later postdoctoral research assistant) provided David with the opportunity to turn to astronomical molecular sources other than molecular clouds. Their work did much to extend the scope of molecular astrophysics. Their first joint paper appeared in 1986 and concerned molecule formation in novae ejecta, while their subsequent pioneering studies have concerned chemistry in T-Tauri winds and supernovae. Work with Tom Millar and David Howe on the chemistry in protoplanetary nebulae and planetary nebulae began to lead to publications in 1992. Lida Nejad contributed to David’s efforts on the study of star-forming regions, and she also helped the wider community through her work on the UMIST astrochemical software. In the early 1990s, Jonathan Rawlings began to work with David on star-formation, and others who were guided by David on these and related problems include Steve Taylor, Ralf Wagenblast, and Karen Willacy. When David moved to UCL in 1994, he was joined by Jonathan Rawlings as a lecturer. David worked on astrophysical problems in a broad range of astronomical environments, but emphasised star formation. However, he did not isolate himself from his new colleagues. With the intelligence and warmth that characterize David, he began to interact with them, and established with experimental and theoretical chemists and physicists a major effort to understand surface reactions relevant to molecular astrophysics. The UCL Centre for Cosmic Chemistry and Physics involves members of three departments at UCL, and is now proving to be very successful in describing the surface reactivity and energetics of hydrogen. He also began a collaboration with Martin McCoustra at the University of Nottingham on surface processes, working initially with Helen Fraser. This programme is now yielding important new results and understanding of desorption from interstellar dirty ices. The first UCL student to complete a doctorate under David’s supervision was Deborah Ruffle, and she played a key role in my collaboration with David in the late 1990s, as have Jonathan Rawlings and Paola Caselli. Serena Viti began a postdoctoral position with David in 1998, and their collaboration has been very productive and included a variety of novel themes. One of these is the illumination of clumps by radiation from Herbig-Haro objects; another is the time-evolution of hot cores. Tammay Nguyen and Phil O’neill also completed doctorates under
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David’s supervision, while Steve Taylor, Andy Lim and Matthew Redman are notable amongst the postdocs who have worked with David at UCL. Molecular astrophysics and astrochemistry remain strong at UCL, thanks to Jonathan Rawlings and to Serena Viti (returning to UCL as a PPARC Advanced Fellow), and to Steve Price (Chemistry) and Andrew Fisher (Physics) and their colleagues in the UCL CCCP. David continues to have many responsibilities to occupy him. In addition to writing a large body of influential research papers, David has been a prolific author and editor of books. His book with John Dyson, The Physics of the Interstellar Medium, first published in 1980, is a classic text used by thousands of researchers and students. It is a remarkably clear and accessible introduction to physics and chemistry that it is important for astronomers to know. His 1984 book with Walt Duley, Interstellar Chemistry, was extremely useful during a key time of growth in the field, and represented the first effort to codify the major area that is its theme. In his several books co-edited with Mark Bailey, with Tom Millar, and with myself, and in one co-authored with me, he successfully extended that effort. David has also played important roles in the national and international astronomical communities as President of the Royal Astronomical Society, as Chairman of the International Astronomical Union’s Working Group on Astrochemistry, as Chair of the Astronomy Committee of PPARC, and the first co-chair of PPARC’s Science Committee. He was invited by Lord Sainsbury to join a three-member Task Force to advise the UK Government on the risk associated with impacts of asteroids and comets on Earth. This job lead to some hilarity in the press, but the Report of the Task Force was well received and helped to present the issue as one that needs to be seriously considered. David has also taken his share of university administration, having been variously Head of Mathematics, Vice-Principal, and Deputy Principal at UMIST, and at UCL he has provided leadership to a group of astronomers with diverse interests. David is a thoughtful, cultured man who is sharing and sensitive to others. He has introduced me to Barsac, and helped me to appreciate the great choral music that he enjoys singing. When we meet, we try to include time for visits to the British Museum, the National Gallery, or Somerset House. I particularly remember an enjoyable walk with him, Jane, and Jonathan on Hampstead Heath and to Kenwood House. Among his various talents is his facility to invent acronyms, displayed most strikingly in the title of a paper co-authored with Walt Duley: HAC IS ERE (or: Hydrogenated Amorphous Carbon InterStellar Extended Red Emission). A list of risque acronyms that were the potential components of a paper with me graced the wall of my Garching office for many years (but are – perhaps – best forgotten). David tends an allotment, though I have seen no evidence of the sweetcorn that he promised me. He also maintains his links with the Unitarian movement, and is a regular preacher, in the humanist tradition. His greatest joy, however, is in his family – with Jane, their sons, daughters-in-law, and grandchildren.
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