Special Issue Preface pubs.acs.org/JPCA
Tribute to Takeshi Oka Applied Chemistry at the Lushun Institute of Technology. As a youth, Oka took inspiration from two great Japanese physicists of the mid-20th century. As he writes, “When I was a high school student in impoverished postwar Japan, the names of Hideki Yukawa and Sin-itiro Tomonaga were two lights in the darkness. They were classmates at Kyoto University, and they received the Nobel Prize for Physics in 1949 and 1965, respectively, for their most fundamental works. Tomonaga was particularly influential...”1 Oka returned to Japan in 1949 and entered the University of Tokyo in 1951, obtaining his Ph.D. in 1960 with Koichi Shimoda and Yonezo Morino in microwave spectroscopy. Oka always felt lucky to have had Shimoda as his mentor, from whom he learned the technique of microwave double-resonance spectroscopy; Shimoda provided him with inspiration for his scientific career. He remained there as a Fellow of the Japanese Society for the Promotion of Science. He was one of several promising young spectroscopists whom Gerhard Herzberg met on a visit to Japan, and he was recruited to NRC by Donald Ramsey in 1962, becoming the first postdoctoral fellow from Japan to join the National Research Council (NRC) in Ottawa, Canada in 1963. Oka became an NRC Research Officer in 1965.2 Oka joined Ramsey, Herzberg, and the large cadre of brilliant young spectroscopists who flocked to the NRC Spectroscopy Laboratory in Ottawa. Those must have been heady days in molecular spectroscopy. (Herzberg was to win the Nobel Prize in Chemistry in 1971.) Oka was given a great deal of independence, and his first papers published from there were all single author. Oka made many pioneering contributions, both experimental and theoretical. These included several experimental studies in microwave double-resonance spectroscopy, the development of the technique of microwave−infrared double-resonance spectroscopy (both on resonance and two-photon) providing tunability at a time when most lasers were fixed in frequency, and exploration of the selection rules for state-changing collisions. In the last, Oka sought to understand the nature of selection rules and distinguish the fundamental from the inexact; in particular, he discovered “forbidden rotational transitions”. In 1968, Oka found his calling in the study of interstellar molecules and began his “45 years in Astrochemistry”, as he describes in the accompanying essay. Among his early observational successes was the first detection of a cyanopolyacetylene. A well-known anecdote is his response when Harry Kroto suggested a collaboration to hunt for HC5N. In a letter dated March 11, 1975, Oka replied:3 “Dear Harry, Thank you for your letter. Yes!! I am very very very very very much interested in your molecule HCC−C C−CN. If you do not mind, please give me B0 for the molecule. If it happens to be in our observing range, I would like to try it. Sincerely yours, Takeshi”
Boyish Oka in his office in September 2011. Behind him are photos of Oka’s idols. The large figure behind Oka is a false color infrared picture of the Galactic center by Shogo Nishiyama and Shuji Sato (reproduced with permission). Portrait of Leonhard Euler by Jakob Emanuel Handmann, 1733 (reproduced with permission of the Kunst Museum, Basel, Switzerland). Portrait of Wolfgang Amadeus Mozart by Josephe Lange, 1789 (reproduced with permission of the Internationale Stiftung Mozarteum, Salzburg, Austria). Photo credit: Lloyd DeGrane, reproduced with permission.
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ith this Festschrift, our community honors Takeshi Oka on the occasion of the 45th anniversary of his entry into the field of astrochemistry. He is known simply as “Oka” to his friends, colleagues, and admirers across the fields of chemistry, physics, and astronomy. Like many of his scientific heroes, Oka brings to science scholarliness, deep physical insight, an appreciation for the beauty of nature and art, a sense of humility and humanity that comes from an awareness of the history of science, and an anarchist’s disregard for authority. The diversity of contributions in this issue reflects both the breadth of Oka’s intellect and the many who have been drawn to him by his generosity, his humanity, and his passionate quest for truth. Oka is perhaps best known for his discovery of the spectrum of H3+, first in the laboratory after years of effort and second in the interstellar medium after 15 years of pursuit. This singular molecule − the simplest polyatomic, comprising three protons and two electrons and possessing D3h symmetry − has been fertile ground for one of the deepest physical thinkers in the field of astrochemistry. It has proved to be the key to some very beautiful and fundamental physics − from the molecular scale to the galactic. Indeed, the laboratory investigations of the fundamental spectroscopic properties of this elegant molecule are tied in surprising and aesthetic ways to the astronomical observations. Dirac would have been pleased. Born in Tokyo, Japan in 1932, Oka spent much of his childhood in Manchuria (Port Arthur (Lushun) and Dalian) as his family followed his father, who founded the Department of © 2013 American Chemical Society
Special Issue: Oka Festschrift: Celebrating 45 Years of Astrochemistry Published: October 3, 2013 9305
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observing H3+ outside the earth was tempered by the lack of success of observing it in interstellar space. Nevertheless, Oka remained confident that detection in an interstellar cloud was possible, a confidence that only increased when a faint infrared quadrupole absorption line of H2 was detected in a dense cloud in 1994. Indeed, in the mid-1990s, the arrival of improved detector arrays and higher resolution spectrographs led to the successful detection of interstellar H3+ in dense clouds in 1996. From that time, a whirlwind of discoveries and revelations has followed and has involved Oka’s students and even a grand-student. Oka’s molecule has turned out to be more than a curiosity of interstellar space; it is now a tool for understanding the physical conditions there. Most notably, it has proven to be a key to understanding the physics and chemistry occurring in diffuse interstellar clouds and in the gas in the innermost regions of the Milky Way. It has also been detected in distant galaxies. One of the things we admire most about Oka is the fertile environment that he provided over the years for his graduate students and postdocs. He was able to strike a perfect balance between giving his group members the independence to pursue their own ideas (and to make and learn from their own mistakes) while at the same time always being available to provide insightful suggestions about both the technical aspects of the experiments and their scientific underpinnings. Oka always looks at problems from a fundamental perspective. Experimentally, he is never satisfied with a surface-level explanation but always drills down to the root. Theoretically, he has the ability to focus on the essential aspects of a problem − either by starting from first principles or by making reasonable simplifying assumptions − and not to be bogged down by details or minor complications. Oka loves to teach; he volunteered to teach general chemistry, even after he had officially retired. More uniquely, Oka brought his strong emphasis on continued learning to his research group. He would lead his students in complete readings of classic textbooks in physics, particularly the Landau & Lifschitz texts, from Mechanics to Electrodynamics of Continuous Media. Every several years, the entire group would go through Volume 3, their classic monograph on quantum mechanics (which seemed to be Oka’s favorite text). Each member would take responsibility for a particular subsection, and the entire group would work through every detail of every derivation, parsing each sentence almost as if it were a religious text. In addition, Oka would often give presentations to the group on fundamental topics, ranging from permutation−inversion group theory to Hönl-London factors. Some might argue that all of this time spent on fundamental learning would detract from scientific productivity, but in our view it forged deeper-thinking and more effective scientists. Oka’s style is quite playful and irreverent. His unbridled joy in pursuing new science, in the lab, at the observatory, or with pencil and paper, has been an inspiration to everyone who has worked with him. He holds a deep admiration for previous work when that work is solid, but he makes his judgments on the basis of the work itself, not on the authority of the author. His irreverence particularly extends to administration: As he tells the story, he was once appointed as the safety officer for a department and proceeded to teach the students that they need to understand what is dangerous in order to respect those dangers. He advocated experiencing mild electric shocks and pouring liquid nitrogen on one’s head so that students would appreciate what they are dealing with. He was promptly removed from duty and was quite relieved. At faculty meetings, he preferred to ignore the
This began a fruitful and important line of research in cyanopolyyne observations. Oka has characteristically always been open to collaboration, without a trace of ego. In Ottawa, Oka began what was to become a lifelong pursuit of the infrared spectrum of H3+. “Herzberg’s enthusiasm on H3+ stimulated me since 1967...I was more influenced by Klemperer’s conjecture of HCO+ and ion chemistry where H3+ plays the pivotal role.” Over the next several years, he built a difference frequency laser system based on the design of Alan Pine and searched tirelessly for the spectrum of H3+. As Herzberg said, “It was my privilege to be there, to watch how he did it, to admire his persistence, and to observe his imagination in gradually finding the best conditions.”4 Ultimate success was achieved in 1980. Impressed by Oka, Steven Berry helped to recruit him in 1981 to The University of Chicago, where Oka held a joint appointment in the Department of Chemistry and the Department of Astronomy and Astrophysics (and later the Enrico Fermi Institute) and was appointed Robert A. Millikan Distinguished Service Professor in 1989. Working with a small group of students and a postdoc, Oka soon turned empty rooms in the basement of Jones Laboratory on South Ellis Avenue into the “Oka Ion Factory”. Oka and his students spent the next decades in fruitful pursuit of laboratory spectra of molecular ions. There was often friendly competition with other labs, but Oka was always generous in his appreciation of the successes and contributions of his “rivals”. His group immediately picked up on the novel velocity modulation technique when it was developed by a young Richard Saykally at Berkeley. In an effort which began as a plan to detect the spectrum of H3+ in irradiated solid hydrogen, he and his group also began a new field, the high-resolution spectroscopy of solid hydrogen and molecules doped in solid hydrogen. Due to the weak interactions, solid hydrogen has proven to be an important new medium for the study of matrix-isolated species, with the infrared spectra of the hydrogen molecules themselves providing information on the intermolecular interactions in the crystal. Oka also continued his observing efforts, especially in search of interstellar H3+. In late 1981, at the suggestion of Charles Townes, he recruited one of us (Geballe), who recalls: “I was unfamiliar with the astrophysical significance of H3+, and I did not know Oka, but his enthusiasm won me over quickly and I am forever grateful that it did.” In the early 1980s, the idea that ion−molecule reactions dominated gas-phase chemistry in dense interstellar clouds was fairly new but already well accepted. However, the cornerstone of that chemistry, and thus its “smoking gun”, H3+, had not been detected. This is not surprising, since the steady-state abundance of H3+ was expected to be low and the spectrum of its fundamental band had only just been measured in the laboratory by Oka. On a few occasions during that decade Oka and Geballe searched for it unsuccessfully. As it turned out, they were using the right observing technique and looking in the right places. However, at that time spectrographs were insufficiently sensitive to detect the weak absorption lines. The upper limits that they obtained were published in 1989; looking back at those spectra now, one can see a 1.5-sigma “detection” in one of the interstellar clouds in which a much more convincing detection was obtained 7 years later. At about the time that the nondetections were published, news came of the totally unexpected discovery that the H3+ overtone band at 2 μm produces bright high-altitude aurorae at the poles of Jupiter. During the next few years, Oka and his colleagues observed the much stronger fundamental band in Jupiter and discovered that band in Saturn as well. The enjoyment of finally 9306
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compelling issues of the day and might quietly derive character tables of permutation groups using Young Tableaux. Oka has always derived great pleasure from the history of physics, and the historical perspective seems to have shaped his own approach to research. He reads extensively, from secondary histories to primary papers. If he disdains the artificial authority of a politician or emperor, he reveres those “heroes” who have made brilliant, creative contributions to science or mathematics while maintaining a sense of humanity. His scholarliness and passion for history and physics can be sensed in casual conversation; it can be seen in his loving translation of The Story of Spin, written by the Japanese physicist Sin-itiro Tomonaga (who won the Nobel Prize in Physics jointly with Richard Feynman and Julian Schwinger for their independent discovery of quantum electrodynamics). His preface to that book begins simply “This book, with the original title Spin wa meguru, is on the physics of spin...It is a mysterious beast, and yet its practical effect prevails over the whole of science. The existence of spin, and the statistics associated with it, is the most subtle and ingenious design of Nature−without it the whole universe would collapse.”1 Oka has run marathons, is fluent in several languages, plays piano, and is a great admirer of Mozart, whose portrait hangs in his office, along with those of Euler, Shimoda, Faraday, Herzberg, and Townes. In addition to shepherding numerous graduate students and postdocs to successful scientific careers, Oka, together with his attentive wife, Keiko, has raised four children. The pursuit of molecular ions and especially H3+ in laboratory physics, astrophysics, and astrochemistry by Oka and others who joined him has been a long and fruitful journey, one full of unexpected discoveries and enlightenments and one that has brought immeasurable surprise, excitement, and a sense of wonder to everyone involved. Throughout this journey, Oka’s insightfulness, his enthusiasm, and his eagerness to learn more have spurred us to persist, work harder, think deeper, and learn everything we can from our data. H3+ has a long and fascinating history, and Oka’s interest in that and indeed the history of all of the physical sciences has continuously added color and context to this scientific adventure and has enriched the lives of his students and colleagues.
Mitchio Okumura California Institute of Technology
Benjamin J. McCall University of Illinois
Thomas R. Geballe
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Gemini Observatory
REFERENCES
(1) Oka, T. Translator’s Preface. In Tomonaga, S. The Story of Spin; The University of Chicago Press: Chicago, 1998; pp viii−xi. (2) Stoicheff, B. P. Gerhard Herzberg: An Illustrious Life in Science; NRC Press: Kingston, Ontario, 2002. (3) Kroto, H. W. Old Spectroscopists Forget a Lot but They Do Remember Their Lines. In Frontiers of Molecular Spectroscopy; Laane, J., Ed.; Elsevier: Amsterdam, 2009; Chapter 1, p 1. (4) Herzberg, G. Foreword. J. Mol. Spectrosc. 1992, 153, 1.
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