MacTutor
David Robert Bates has been described as probably the greatest Irish scientist of the present century. He gained world renown for his work in atomic and molecular physics, for his studies of the Earth's upper atmosphere, and for his contributions to astronomy. He was awarded our Gold Medal in 1977, having been a Fellow of the Society since 1947.
David's father, Walter Vivian Bates, came from Mountrath in County Laois, Southern Ireland. He served an apprenticeship as a pharmacist in Dundalk and then moved to Omagh, a small Ulster country town, in 1909 where he had a chemist's shop. In 1911, he married Mary Olive Shera, who came from a family of farming folk, and David Robert was born on November 18, 1916, the second of two surviving children. He and his sister Margaret attended Miss Quigley's one-room school until David was nine, when his mother moved with them to Belfast seeking better educational prospects for them. Many years later, David wrote, "I accepted the move thoughtlessly, not then appreciating the sacrifice made by my father, who continued his business as a pharmacist in Omagh, traveling to our home in Belfast twice a week." (1) It is a curious coincidence that a similar sacrifice was made by Harrie Massey's father. (2)
David attended the Inchmarlo preparatory school before entering the Royal Belfast Academical Institution, where he delighted in the excellence of the teaching in mathematics and science but received public rebuke for his lack of enthusiasm for organized games. He entered the Queen's University of Belfast in 1934, where he was enticed away from chemistry by the superb lectures of George Emeleus in experimental physics and Harrie Massey in mathematical physics. On graduating, he registered for an MSc degree in theoretical physics, under Massey's supervision, but also did a substantial piece of experimental work on the spectra of gas discharges
Advances in upper-atmosphere physics, as in most other branches of geophysics and astronomy, depend essentially on the participation of researchers with deep and specialized knowledge of many different branches of science. Massey and his small group in Belfast were the pioneers in making detailed studies of atomic and molecular processes in the Earth's upper atmosphere. In the autumn of 1938, Massey was appointed to a chair of Applied Mathematics at University College London: David made the move with him and registered for a PhD degree at UCL. Due to the coming of the war, the PhD thesis was never submitted, but by 1950, David had published many important papers, and the University of London recognized a Belfast MSc as an adequate qualifying examination for the award of a DSc.
At the start of the war, a major threat was the German magnetic mine campaign against British shipping. Massey's help was enlisted, and he went to work at the Admiralty Research Laboratory in Teddington, once again taking David Bates with him. It was a remarkable team at ARL including, in addition to Massey and Bates, N.F.Barber, R.A.Buckingham, S. Butterworth, F.H.C.Crick and J.C.Gunn. Their work is described by Sir John Gunn in a contribution to a Biographical Memoir for Massey (2) and in a further letter to me. Bates and Crick worked in a non-magnetic hut in the grounds of ARL, making comprehensive measurements of the magnetic fields of model ships, while Buckingham and Gunn did theoretical work on fields of ships and mine sweeps. By early 1941 the problems of defence against enemy mines were largely solved and the group went over to the offensive, moving to the Mine Design Department of HMS Vernon near Portsmouth. Bates was concerned with intensely practical problems, such as the design of packing sensitive instruments on mines in such a way as to avoid damage from shocks during aircraft drops (he later described the work as mechanical engineering sufficiently difficult to be interesting). Francis Crick writes, "Beneath a quiet, rather reserved manner, David seemed confident in himself, with a shy, rather engaging charm ... like John Gunn, I recall my association with him with affection."
In 1945, David returned to UCL as a lecturer, and I first met him a year later when I found Mr. Bates's lectures on ancillary mathematics to be a highlight of my undergraduate physics course (later on, of course, he was Professor Sir David, knighted in 1978). During the war years, he had managed to continue with some academic research, and in the years immediately following, his output was prolific. He described 1950, which he spent in the United States working with, among others, Marcel Nicolet and Lyman Spitzer, as one of the best years of his life.
In 1951, David Bates was appointed to a newly created chair of Applied Mathematics at Queen's University Belfast During those early years after his return to QUB I once asked him why he worked so incredibly hard: he replied "because of my love of Ulster". It was a love for all of Ulster's people that led to deep concern for their welfare. He recalled his childhood as a period of terrible civil war yet how, at that time, his closest playmates came from families committed to opposite sides in the conflict. Writing of his students, he would not say "Catholics" and "Protestants", but those "nourished by our two different traditions". When the troubles erupted to new levels of violence in the 1970s David was not one to stand aside. He was a founding member of the Alliance Party, the only major political party in Northern Ireland to be strictly non-sectarian, and he served as its Vice-President for the rest of his life. He would have rejoiced at the new initiatives for peace and reconciliation which were publicly announced not long after his death on January 5, 1994. He bequeathed to his beloved Province the QUB Department of Applied Mathematics and Theoretical Physics with an established reputation as the world's leading centre for theoretical studies in atomic and molecular physics and for the calculation of atomic and molecular data needed in astronomy and aeronomy.
In 1955, David was elected to the Fellowship of the Royal Society. While in London for the admission ceremony, he met Barbara Morris at the home of a mutual friend and not long afterwards made a formal proposal of marriage (Barbara tells me that this was behind the book stacks in the Society's library, then in Burlington House). Harrie Massey, in a Festschrift volume for David's 60th birthday (3), wrote: "In 1956 my wife and I had the privilege of attending his wedding to Barbara. After the ceremony we lunched at the Coq d'Or and then, while Barbara and my wife looked at the shops, Bates and I attended a meeting of the Gassiot Committee ...". Robert Boyd arrived at the meeting and solemnly handed over an envelope full of confetti. The Gassiot Committee notwithstanding, all who knew David and know Barbara never had any doubt that March 20, 1956 was by far the most important date in David's life. They had two children, Katharine, who is now a show jumper, and Adam, who works in London as an accountant and looks remarkably like his father. Many of us cherish memories of the splendid hospitality we have so often received at the home of Barbara and David.
In early 1974, David had a serious heart attack When recovered his doctor told him that, provided he took life more easily, he would have another 20 years to live. By that time he had built his Department up to a strength where his position as its administrative head was no longer essential. He resigned from that position and from other administrative posts. He found more time to walk his dog and to chat at leisure with staff and students over morning coffee in the Department's Common Room (on my many visits I would be told "see, David is holding court"). He also adopted a hobby, the study of making contact with extra-terrestrial civilizations and made one firm prediction: "NASA's SETI will not pick up a message ... the reasons are rooted in the inescapable tyranny of time". Yet obeying doctor's orders did not mean an end to research. After 1973 David published a further 140 papers, many of them highly original and breaking new ground. When in 1985 the Department's building was named after him, he remarked that it was good to see one's name over the shop: not everyone knew he was thinking of the pharmacy in Omagh.
Let me return to 1937. One problem was to understand rates of recombination in the ionosphere. Unlike the solar corona, where recombination rates can only be deduced indirectly from studies of the ionization balance, rates for the ionosphere can be deduced directly from diurnal variations and from eclipse measurements. Electrons do not just stick to positive ions: the reaction A++eA will not go because it cannot simultaneously conserve both energy and momentum. Sydney Chapman had suggested that the reaction might be radiative recombination, A++eA*+hv (one must sum over all possible final states A* of A). Bates' first research task was to calculate rates for that process. The work was done in collaboration with his close friend J.J. Unwin (who was killed in a flying accident early in the war). Bates later estimated that over 1000 hours of computing time were required using five-figure log tables. This turned out that rates for radiative recombination were too small, by several orders of magnitude, to explain the ionospheric results. In 1947, Bates and Massey returned to the problem and suggested that the processes might be charge-transfer to form molecular ions, , followed by dissociative recombination, , but it was not until 1950 that Bates showed that the latter process could, indeed, be sufficiently rapid. There are many variants to these processes. In place of charge-transfer, one can have ion-atom interchange, . In later work in interstellar chemistry, Bates devoted a lot of effort to discussing the possible, and most probable, products formed in dissociative recombination of polyatomic ions. Incidentally, the problem of the ionization balance in the solar corona was finally resolved by Alan Burgess, on making further developments in the theory of di-electronic recombination first formulated by Bates and Massey. Another problem which occupied the early chemical aeronomists was the determination of the number of negative ions in the ionosphere. The problem arose in connection with studies of diurnal and semi-diurnal variations in the Earth's magnetic field produced by tidal motions in the ionosphere. In 1927 Pedersen had estimated the ionospheric electrical conductivity making some allowance for the effects of a magnetic field and found that it would be much too low if the charge density were that deduced from radio measurements of electron density. It was therefore proposed by Pedersen and Chapman - and widely believed for many years - that the number of negative ions might exceed the number of electrons by a factor λ of the order 100 to 1000 or even larger, and this led to detailed studies of processes providing formation and destruction of negative ions. By 1947 Bates and Massey concluded that the whole idea of large concentrations of negative ions was untenable: they wrote "the smallness of the important ratio λ would seem inescapable". That stimulated further work on the magnetic field variations which led to new ideas concerning the magneto-hydrodynamics of current flow in the presence of magnetic fields.
Although the number density of sodium atoms is very low in the upper atmosphere, radiation in the Na+D lines is observed at twilight due to the great efficiency of the scattering process. In 1950, Bates suggested the use of rockets to eject grenades, which would produce localized sodium clouds, and estimated that an artificial cloud containing 1 kg of sodium vapor would produce an illumination comparable to that of the full moon. The experiment was included as part of the British Space Research Program, and in subsequent years, such artificial clouds have been used extensively in studies of upper-atmosphere winds. The media seized on the first press release about the entire British program: "Artificial Moonlight", and even "Courting by Artificial Moonlight". Barbara and David did not issue a public announcement of their intention to marry, but the media were as alert as ever: "Moonlight Professor Weds in Secret".
Whenever a defense is needed for expenditure on research, I like to stand in full square with my colleagues in, say, classical archaeology: any civilized society should be prepared to spend some small part of its wealth in the pursuit of research and learning. It is only when the greater expenditure on science is noted that there need be resort to the further argument: you never know when knowledge might come in handy. Chemical aeronomy provides a very good example illustrating that case. The pioneers were not concerned with greenhouse effects or ozone holes, yet when those topics became of general concern, the public could be very glad that some basic research had already been done. Three papers by Bates deserve particular mention. First, that with Nicolet in 1950 on atmospheric water, which included a discussion of mechanisms leading to the formation and destruction of hydroxyl, OH, and its interactions with ozone. Second, the 1952 paper with Agnes Witherspoon on the photochemistry of some minor constituents
of the Earth's atmosphere. Writing in 1976, Michael McElroy (another of David's former students) said that paper was "a classic contribution, required reading for all who might wish to study man's impact on the global atmospheric environment." And third, the 1967 paper with P.B. Hays on atmospheric nitrous oxide, which emphasized the role of microbiology as a source for NO and considered photodissociation as the primary sink.
For those who have entered the field of upper-atmosphere physics only in more recent years, it may be difficult to appreciate just how meager the information available to the early workers was. The main sources of information were radio soundings; geomagnetic variations; and studies of spectral emissions from the night sky and aurorae. It was generally believed that the ionospheric layers were formed by ultraviolet light producing photoionization. Lacking a better guide, the Sun was assumed to radiate like a 6000 K blackbody, even in the UV It was not too difficult to explain the higher, F, layer as being due to photo-ionisation of atomic oxygen. In 1939 Bates made the first calculation of the O photo-ionisation cross-section and later work has shown his results to be surprisingly accurate (nature is sometimes kind in that a comparatively simple treatment gives a good result). Development of a satisfactory theory for the lower, E and D, layers took a lot longer. In 1948 Fred Hoyle and David Bates considered the possibility that solar X-rays might contribute to E-region formation. Later it was established that X-rays do indeed contribute but are only really important at times of solar maximum.
The use of rockets and satellites utterly changed the nature of upper-atmosphere research. With them, one can make in situ measurements of temperatures, of number densities of all the atomic, molecular, and ionic constituents, and continuously monitor the solar radiation at UV and X-ray wavelengths. There have been corresponding developments in experimental work and in making computations: some of us still keep our five-figure log tables, but we rarely take them down from their shelves.
The problem of the height of emission of the radiations from the night sky provides one example of how quickly a contentious issue could be settled once direct measurements could be made. Using a method suggested by van Rhijn in 1921, it should be possible to deduce the emission height from measurements of observed intensities as functions of zenith angle. As a major advance over the use of photographic techniques, early photoelectric photometers were first employed in the 1950s. Emission heights of the order of 250 km were obtained Bates and Nicolet in 1950 and Bates and Dalgarno in 1953 argued that it was inconceivable that such great heights could be correct: the required photochemical rates just might not be large enough. The matter was settled in 1956 using photometers looking out of windows in rockets. That gave maximum emission at 100 km, just where the theoreticians had said it should be. Further van Rhijn measurements soon gave results in agreement, once some errors in the calibrations of the photometers had been corrected! There are still many unsolved problems concerning details of the night-sky emissions, and David Bates was working on them to the end of his life.
What were the characteristics of his work? First, highly original thinking in trying to see possible solutions to difficult problems. Second, relentless pursuit of all the facts and study of all original sources (I liked his footnote to a long list of references: "This is a correction to the 1912 paper. Some writers innocently refer to it as if it had appeared in the non-existent journal Berichtigung"). And third, great mathematical and computational skill in solving problems, particularly those in atomic and molecular physics. This would not be the place to give much detail concerning the physics work, but some highlights must be mentioned.
In his early work, Bates made many important calculations of cross-sections for photoionization and photodetachment. His 1946 Monthly Notices of the Royal Astronomical Society review was a landmark in that field. And if negative ions turned out, after all, not to be of much importance in the ionosphere, they did prove to be important elsewhere. In 1939, P. Wildt suggested that provides the main source of continuous absorption in the solar atmosphere, and Massey and Bates in 1940 made the first detailed quantum mechanical calculation for the process Agnete Damgaard, a Danish woman, was David's first research student at UCL (I came second). The 1949 paper by Bates and Damgaard on the calculation of oscillator strengths quickly became a citation classic. The results were only approximate (except for the simplest alkali-like systems) but the work proved to be enormously useful because it enabled estimates to be made for large numbers of transitions. It was warmly welcomed by M.G.J.Minnaert and others in desperate need of oscillator strengths for the analysis of solar and stellar spectra.
In 1950, David could not have spent very long in Princeton, but while there, he did two pieces of work of major importance: one on the theory of dissociative recombination; and a pioneering study with Lyman Spitzer on the formation and destruction of interstellar molecules. How can such molecules be formed at the very low densities of interstellar space? If there are no seed molecules and no dust, just about the only possible process is radiative attachment, . David gave a detailed treatment of the theory for that process, in which he showed that previous work had given rate coefficients a good deal too large. To celebrate his 70th birthday, he wrote a magnificent review (4) of his later work on interstellar chemistry, which included studies of many processes involving polyatomic molecules
Ab initio studies of atomic collision processes are important both because they provide estimates of rate coefficients of importance for astronomy, aeronomy, and fusion research, and because they provide firm foundations for all studies of chemical reactions. David Bates never did a great deal of work on electron collisions, but he did encourage such work by others, and the achievements of the team led by Phil Burke have greatly added to the prestige of the Belfast Department. Calculations for processes involving heavier particles, even for a simple case such as collisions between protons and H atoms, are fraught with difficulties. A standard approach in chemistry is to take advantage of the fact that electrons move much more rapidly than nuclei and hence to obtain a first approximation for electron motions assuming the nuclei to be at rest (the Born-Oppenheimer approximation). Working in collaboration with Ron McCarroll and other students at QUB, David developed the method of perturbed stationary states for collision problems. There was always a difficulty in obtaining functions with correct asymptotic forms, and a great deal of further work was required. Nevertheless, the methods proposed at QUB in 1957 provided an essential starting point.
David did a great deal to promote the dissemination of scientific knowledge. Once asked whether too many papers were published, he replied no; they fall to the forest floor and act like humus in promoting new growth. He was Founding Editor of Advances in Atomic, Molecular and Optical Physics and continued as Editor (ably assisted first by Immanuel Estermann and later by Ben Bedersen) until 1993. In 1994, Bedersen wrote, "The fact that the tables of contents of the Advances series virtually track the history of these fields over the past 30 years is no accident—it reflects Sir David's own professional history, which is so intertwined with the general history of these fields as to be virtually inseparable." He was also Editor-in-Chief of Planetary and Space Science from 1961 until 1992 (after that date the journal continued proudly to print his name as Editor Emeritus). Desmond King-Hele, also closely associated with that journal, writes: "I always admired him as the beau idéal of a scientific editor: wise, perceptive, efficient, and benign."
Sir David Bates published over 330 scientific papers. He received honorary degrees from the Universities of Belfast, Dublin, Essex, Glasgow, the National University of Ireland, Stirling, Ulster, York (Ontario), and York (England). In addition to our Gold Medal, which I have already mentioned, he received the Hughes Medal of the Royal Society in 1970, the Chree Medal of the Institute of Physics in 1973, and the Fleming Medal of the American Geophysical Union in 1987. He was a Foreign Member of the American Academy of Arts and Sciences, an Associate Member of the Royal Academy of Belgium, and an Honorary Member of the European Geophysical Union, which established a Medal in his name in 1992.
MICHAEL J. SEATON
References
(1) Bates, D.R., 1983. Scientific reminiscences, Int. J. Quant. Chem., 17, 4
(2) Bates, D.R., Boyd, R.L.F. and Davis, D.G., 1984. Harrie Stewart Wilson Massey, 1908–1983, Biog. Mem. Fell. Roy. Soc., 30, 445.
(3) Massey, H.S.W.. D.R. Bates: A Sixteenth Birthday Tribute. In Atomic and Molecular Processes, eds. Burke, P.G. & Moiseiwitsch, B.L., North-Holland, Amsterdam (1976).
(4) Bates, D.R.. Interstellar Cloud Chemistry Revisited. In Recent Studies in Atomic and Molecular Processes, ed. Kingston, A.E., Plenum Press, London (1987)
David's father, Walter Vivian Bates, came from Mountrath in County Laois, Southern Ireland. He served an apprenticeship as a pharmacist in Dundalk and then moved to Omagh, a small Ulster country town, in 1909 where he had a chemist's shop. In 1911, he married Mary Olive Shera, who came from a family of farming folk, and David Robert was born on November 18, 1916, the second of two surviving children. He and his sister Margaret attended Miss Quigley's one-room school until David was nine, when his mother moved with them to Belfast seeking better educational prospects for them. Many years later, David wrote, "I accepted the move thoughtlessly, not then appreciating the sacrifice made by my father, who continued his business as a pharmacist in Omagh, traveling to our home in Belfast twice a week." (1) It is a curious coincidence that a similar sacrifice was made by Harrie Massey's father. (2)
David attended the Inchmarlo preparatory school before entering the Royal Belfast Academical Institution, where he delighted in the excellence of the teaching in mathematics and science but received public rebuke for his lack of enthusiasm for organized games. He entered the Queen's University of Belfast in 1934, where he was enticed away from chemistry by the superb lectures of George Emeleus in experimental physics and Harrie Massey in mathematical physics. On graduating, he registered for an MSc degree in theoretical physics, under Massey's supervision, but also did a substantial piece of experimental work on the spectra of gas discharges
Advances in upper-atmosphere physics, as in most other branches of geophysics and astronomy, depend essentially on the participation of researchers with deep and specialized knowledge of many different branches of science. Massey and his small group in Belfast were the pioneers in making detailed studies of atomic and molecular processes in the Earth's upper atmosphere. In the autumn of 1938, Massey was appointed to a chair of Applied Mathematics at University College London: David made the move with him and registered for a PhD degree at UCL. Due to the coming of the war, the PhD thesis was never submitted, but by 1950, David had published many important papers, and the University of London recognized a Belfast MSc as an adequate qualifying examination for the award of a DSc.
At the start of the war, a major threat was the German magnetic mine campaign against British shipping. Massey's help was enlisted, and he went to work at the Admiralty Research Laboratory in Teddington, once again taking David Bates with him. It was a remarkable team at ARL including, in addition to Massey and Bates, N.F.Barber, R.A.Buckingham, S. Butterworth, F.H.C.Crick and J.C.Gunn. Their work is described by Sir John Gunn in a contribution to a Biographical Memoir for Massey (2) and in a further letter to me. Bates and Crick worked in a non-magnetic hut in the grounds of ARL, making comprehensive measurements of the magnetic fields of model ships, while Buckingham and Gunn did theoretical work on fields of ships and mine sweeps. By early 1941 the problems of defence against enemy mines were largely solved and the group went over to the offensive, moving to the Mine Design Department of HMS Vernon near Portsmouth. Bates was concerned with intensely practical problems, such as the design of packing sensitive instruments on mines in such a way as to avoid damage from shocks during aircraft drops (he later described the work as mechanical engineering sufficiently difficult to be interesting). Francis Crick writes, "Beneath a quiet, rather reserved manner, David seemed confident in himself, with a shy, rather engaging charm ... like John Gunn, I recall my association with him with affection."
In 1945, David returned to UCL as a lecturer, and I first met him a year later when I found Mr. Bates's lectures on ancillary mathematics to be a highlight of my undergraduate physics course (later on, of course, he was Professor Sir David, knighted in 1978). During the war years, he had managed to continue with some academic research, and in the years immediately following, his output was prolific. He described 1950, which he spent in the United States working with, among others, Marcel Nicolet and Lyman Spitzer, as one of the best years of his life.
In 1951, David Bates was appointed to a newly created chair of Applied Mathematics at Queen's University Belfast During those early years after his return to QUB I once asked him why he worked so incredibly hard: he replied "because of my love of Ulster". It was a love for all of Ulster's people that led to deep concern for their welfare. He recalled his childhood as a period of terrible civil war yet how, at that time, his closest playmates came from families committed to opposite sides in the conflict. Writing of his students, he would not say "Catholics" and "Protestants", but those "nourished by our two different traditions". When the troubles erupted to new levels of violence in the 1970s David was not one to stand aside. He was a founding member of the Alliance Party, the only major political party in Northern Ireland to be strictly non-sectarian, and he served as its Vice-President for the rest of his life. He would have rejoiced at the new initiatives for peace and reconciliation which were publicly announced not long after his death on January 5, 1994. He bequeathed to his beloved Province the QUB Department of Applied Mathematics and Theoretical Physics with an established reputation as the world's leading centre for theoretical studies in atomic and molecular physics and for the calculation of atomic and molecular data needed in astronomy and aeronomy.
In 1955, David was elected to the Fellowship of the Royal Society. While in London for the admission ceremony, he met Barbara Morris at the home of a mutual friend and not long afterwards made a formal proposal of marriage (Barbara tells me that this was behind the book stacks in the Society's library, then in Burlington House). Harrie Massey, in a Festschrift volume for David's 60th birthday (3), wrote: "In 1956 my wife and I had the privilege of attending his wedding to Barbara. After the ceremony we lunched at the Coq d'Or and then, while Barbara and my wife looked at the shops, Bates and I attended a meeting of the Gassiot Committee ...". Robert Boyd arrived at the meeting and solemnly handed over an envelope full of confetti. The Gassiot Committee notwithstanding, all who knew David and know Barbara never had any doubt that March 20, 1956 was by far the most important date in David's life. They had two children, Katharine, who is now a show jumper, and Adam, who works in London as an accountant and looks remarkably like his father. Many of us cherish memories of the splendid hospitality we have so often received at the home of Barbara and David.
In early 1974, David had a serious heart attack When recovered his doctor told him that, provided he took life more easily, he would have another 20 years to live. By that time he had built his Department up to a strength where his position as its administrative head was no longer essential. He resigned from that position and from other administrative posts. He found more time to walk his dog and to chat at leisure with staff and students over morning coffee in the Department's Common Room (on my many visits I would be told "see, David is holding court"). He also adopted a hobby, the study of making contact with extra-terrestrial civilizations and made one firm prediction: "NASA's SETI will not pick up a message ... the reasons are rooted in the inescapable tyranny of time". Yet obeying doctor's orders did not mean an end to research. After 1973 David published a further 140 papers, many of them highly original and breaking new ground. When in 1985 the Department's building was named after him, he remarked that it was good to see one's name over the shop: not everyone knew he was thinking of the pharmacy in Omagh.
Let me return to 1937. One problem was to understand rates of recombination in the ionosphere. Unlike the solar corona, where recombination rates can only be deduced indirectly from studies of the ionization balance, rates for the ionosphere can be deduced directly from diurnal variations and from eclipse measurements. Electrons do not just stick to positive ions: the reaction A++eA will not go because it cannot simultaneously conserve both energy and momentum. Sydney Chapman had suggested that the reaction might be radiative recombination, A++eA*+hv (one must sum over all possible final states A* of A). Bates' first research task was to calculate rates for that process. The work was done in collaboration with his close friend J.J. Unwin (who was killed in a flying accident early in the war). Bates later estimated that over 1000 hours of computing time were required using five-figure log tables. This turned out that rates for radiative recombination were too small, by several orders of magnitude, to explain the ionospheric results. In 1947, Bates and Massey returned to the problem and suggested that the processes might be charge-transfer to form molecular ions, , followed by dissociative recombination, , but it was not until 1950 that Bates showed that the latter process could, indeed, be sufficiently rapid. There are many variants to these processes. In place of charge-transfer, one can have ion-atom interchange, . In later work in interstellar chemistry, Bates devoted a lot of effort to discussing the possible, and most probable, products formed in dissociative recombination of polyatomic ions. Incidentally, the problem of the ionization balance in the solar corona was finally resolved by Alan Burgess, on making further developments in the theory of di-electronic recombination first formulated by Bates and Massey. Another problem which occupied the early chemical aeronomists was the determination of the number of negative ions in the ionosphere. The problem arose in connection with studies of diurnal and semi-diurnal variations in the Earth's magnetic field produced by tidal motions in the ionosphere. In 1927 Pedersen had estimated the ionospheric electrical conductivity making some allowance for the effects of a magnetic field and found that it would be much too low if the charge density were that deduced from radio measurements of electron density. It was therefore proposed by Pedersen and Chapman - and widely believed for many years - that the number of negative ions might exceed the number of electrons by a factor λ of the order 100 to 1000 or even larger, and this led to detailed studies of processes providing formation and destruction of negative ions. By 1947 Bates and Massey concluded that the whole idea of large concentrations of negative ions was untenable: they wrote "the smallness of the important ratio λ would seem inescapable". That stimulated further work on the magnetic field variations which led to new ideas concerning the magneto-hydrodynamics of current flow in the presence of magnetic fields.
Although the number density of sodium atoms is very low in the upper atmosphere, radiation in the Na+D lines is observed at twilight due to the great efficiency of the scattering process. In 1950, Bates suggested the use of rockets to eject grenades, which would produce localized sodium clouds, and estimated that an artificial cloud containing 1 kg of sodium vapor would produce an illumination comparable to that of the full moon. The experiment was included as part of the British Space Research Program, and in subsequent years, such artificial clouds have been used extensively in studies of upper-atmosphere winds. The media seized on the first press release about the entire British program: "Artificial Moonlight", and even "Courting by Artificial Moonlight". Barbara and David did not issue a public announcement of their intention to marry, but the media were as alert as ever: "Moonlight Professor Weds in Secret".
Whenever a defense is needed for expenditure on research, I like to stand in full square with my colleagues in, say, classical archaeology: any civilized society should be prepared to spend some small part of its wealth in the pursuit of research and learning. It is only when the greater expenditure on science is noted that there need be resort to the further argument: you never know when knowledge might come in handy. Chemical aeronomy provides a very good example illustrating that case. The pioneers were not concerned with greenhouse effects or ozone holes, yet when those topics became of general concern, the public could be very glad that some basic research had already been done. Three papers by Bates deserve particular mention. First, that with Nicolet in 1950 on atmospheric water, which included a discussion of mechanisms leading to the formation and destruction of hydroxyl, OH, and its interactions with ozone. Second, the 1952 paper with Agnes Witherspoon on the photochemistry of some minor constituents
of the Earth's atmosphere. Writing in 1976, Michael McElroy (another of David's former students) said that paper was "a classic contribution, required reading for all who might wish to study man's impact on the global atmospheric environment." And third, the 1967 paper with P.B. Hays on atmospheric nitrous oxide, which emphasized the role of microbiology as a source for NO and considered photodissociation as the primary sink.
For those who have entered the field of upper-atmosphere physics only in more recent years, it may be difficult to appreciate just how meager the information available to the early workers was. The main sources of information were radio soundings; geomagnetic variations; and studies of spectral emissions from the night sky and aurorae. It was generally believed that the ionospheric layers were formed by ultraviolet light producing photoionization. Lacking a better guide, the Sun was assumed to radiate like a 6000 K blackbody, even in the UV It was not too difficult to explain the higher, F, layer as being due to photo-ionisation of atomic oxygen. In 1939 Bates made the first calculation of the O photo-ionisation cross-section and later work has shown his results to be surprisingly accurate (nature is sometimes kind in that a comparatively simple treatment gives a good result). Development of a satisfactory theory for the lower, E and D, layers took a lot longer. In 1948 Fred Hoyle and David Bates considered the possibility that solar X-rays might contribute to E-region formation. Later it was established that X-rays do indeed contribute but are only really important at times of solar maximum.
The use of rockets and satellites utterly changed the nature of upper-atmosphere research. With them, one can make in situ measurements of temperatures, of number densities of all the atomic, molecular, and ionic constituents, and continuously monitor the solar radiation at UV and X-ray wavelengths. There have been corresponding developments in experimental work and in making computations: some of us still keep our five-figure log tables, but we rarely take them down from their shelves.
The problem of the height of emission of the radiations from the night sky provides one example of how quickly a contentious issue could be settled once direct measurements could be made. Using a method suggested by van Rhijn in 1921, it should be possible to deduce the emission height from measurements of observed intensities as functions of zenith angle. As a major advance over the use of photographic techniques, early photoelectric photometers were first employed in the 1950s. Emission heights of the order of 250 km were obtained Bates and Nicolet in 1950 and Bates and Dalgarno in 1953 argued that it was inconceivable that such great heights could be correct: the required photochemical rates just might not be large enough. The matter was settled in 1956 using photometers looking out of windows in rockets. That gave maximum emission at 100 km, just where the theoreticians had said it should be. Further van Rhijn measurements soon gave results in agreement, once some errors in the calibrations of the photometers had been corrected! There are still many unsolved problems concerning details of the night-sky emissions, and David Bates was working on them to the end of his life.
What were the characteristics of his work? First, highly original thinking in trying to see possible solutions to difficult problems. Second, relentless pursuit of all the facts and study of all original sources (I liked his footnote to a long list of references: "This is a correction to the 1912 paper. Some writers innocently refer to it as if it had appeared in the non-existent journal Berichtigung"). And third, great mathematical and computational skill in solving problems, particularly those in atomic and molecular physics. This would not be the place to give much detail concerning the physics work, but some highlights must be mentioned.
In his early work, Bates made many important calculations of cross-sections for photoionization and photodetachment. His 1946 Monthly Notices of the Royal Astronomical Society review was a landmark in that field. And if negative ions turned out, after all, not to be of much importance in the ionosphere, they did prove to be important elsewhere. In 1939, P. Wildt suggested that provides the main source of continuous absorption in the solar atmosphere, and Massey and Bates in 1940 made the first detailed quantum mechanical calculation for the process Agnete Damgaard, a Danish woman, was David's first research student at UCL (I came second). The 1949 paper by Bates and Damgaard on the calculation of oscillator strengths quickly became a citation classic. The results were only approximate (except for the simplest alkali-like systems) but the work proved to be enormously useful because it enabled estimates to be made for large numbers of transitions. It was warmly welcomed by M.G.J.Minnaert and others in desperate need of oscillator strengths for the analysis of solar and stellar spectra.
In 1950, David could not have spent very long in Princeton, but while there, he did two pieces of work of major importance: one on the theory of dissociative recombination; and a pioneering study with Lyman Spitzer on the formation and destruction of interstellar molecules. How can such molecules be formed at the very low densities of interstellar space? If there are no seed molecules and no dust, just about the only possible process is radiative attachment, . David gave a detailed treatment of the theory for that process, in which he showed that previous work had given rate coefficients a good deal too large. To celebrate his 70th birthday, he wrote a magnificent review (4) of his later work on interstellar chemistry, which included studies of many processes involving polyatomic molecules
Ab initio studies of atomic collision processes are important both because they provide estimates of rate coefficients of importance for astronomy, aeronomy, and fusion research, and because they provide firm foundations for all studies of chemical reactions. David Bates never did a great deal of work on electron collisions, but he did encourage such work by others, and the achievements of the team led by Phil Burke have greatly added to the prestige of the Belfast Department. Calculations for processes involving heavier particles, even for a simple case such as collisions between protons and H atoms, are fraught with difficulties. A standard approach in chemistry is to take advantage of the fact that electrons move much more rapidly than nuclei and hence to obtain a first approximation for electron motions assuming the nuclei to be at rest (the Born-Oppenheimer approximation). Working in collaboration with Ron McCarroll and other students at QUB, David developed the method of perturbed stationary states for collision problems. There was always a difficulty in obtaining functions with correct asymptotic forms, and a great deal of further work was required. Nevertheless, the methods proposed at QUB in 1957 provided an essential starting point.
David did a great deal to promote the dissemination of scientific knowledge. Once asked whether too many papers were published, he replied no; they fall to the forest floor and act like humus in promoting new growth. He was Founding Editor of Advances in Atomic, Molecular and Optical Physics and continued as Editor (ably assisted first by Immanuel Estermann and later by Ben Bedersen) until 1993. In 1994, Bedersen wrote, "The fact that the tables of contents of the Advances series virtually track the history of these fields over the past 30 years is no accident—it reflects Sir David's own professional history, which is so intertwined with the general history of these fields as to be virtually inseparable." He was also Editor-in-Chief of Planetary and Space Science from 1961 until 1992 (after that date the journal continued proudly to print his name as Editor Emeritus). Desmond King-Hele, also closely associated with that journal, writes: "I always admired him as the beau idéal of a scientific editor: wise, perceptive, efficient, and benign."
Sir David Bates published over 330 scientific papers. He received honorary degrees from the Universities of Belfast, Dublin, Essex, Glasgow, the National University of Ireland, Stirling, Ulster, York (Ontario), and York (England). In addition to our Gold Medal, which I have already mentioned, he received the Hughes Medal of the Royal Society in 1970, the Chree Medal of the Institute of Physics in 1973, and the Fleming Medal of the American Geophysical Union in 1987. He was a Foreign Member of the American Academy of Arts and Sciences, an Associate Member of the Royal Academy of Belgium, and an Honorary Member of the European Geophysical Union, which established a Medal in his name in 1992.
MICHAEL J. SEATON
References
(1) Bates, D.R., 1983. Scientific reminiscences, Int. J. Quant. Chem., 17, 4
(2) Bates, D.R., Boyd, R.L.F. and Davis, D.G., 1984. Harrie Stewart Wilson Massey, 1908–1983, Biog. Mem. Fell. Roy. Soc., 30, 445.
(3) Massey, H.S.W.. D.R. Bates: A Sixteenth Birthday Tribute. In Atomic and Molecular Processes, eds. Burke, P.G. & Moiseiwitsch, B.L., North-Holland, Amsterdam (1976).
(4) Bates, D.R.. Interstellar Cloud Chemistry Revisited. In Recent Studies in Atomic and Molecular Processes, ed. Kingston, A.E., Plenum Press, London (1987)
David Robert Bates's obituary appeared in Jornal of the Royal Astronomical Society 37:1 (1996), 81-87.