Mihir Chowdhury (1937–2017): Scientist and Teacher Extraordinaire
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PERSONAL NEWS Mihir Chowdhury (1937–2017): scientist and teacher extraordinaire Scientific and technical biography throwing light on how Mihir Chowdhury’s research interest evolved dur- ing his active years in science and how he innovated in both teaching and research. Henry Smith wrote ‘A teacher can affect (1966–76) of his tenure there. At the teaching even during the busiest part of eternity; he does not know when his in- same time, he was moving to IACS to his career as a scientist. He was no ora- fluence comes to an end’. The sad de- succeed Professor S. R. Palit, the undis- tor; it was the depth of his analysis and mise of Professor Mihir Chowdhury puted emperor of polymer chemistry in crisp logic-based articulation of a subject (formerly Head, Department of Physical India in those days. The Department was from scratch that enthralled the students Chemistry, Indian Association for the indeed well known for its contributions and made the classroom alive. Cultivation of Science (IACS), Kolkata) to polymer and solution chemistry. on 28 March 2017 brought to the fore the Chowdhury’s task was cut out: he would deep truth of Smith’s observation1. Pro- have to reshape, remodel and refashion The scientist tracted and debilitating illness kept him the Department into a modern centre of away from active science for over a dec- physical chemistry. He had the clear The research activities of Chowdhury ade or so; yet the news of his passing vision and meticulous planning that the were varied, full of ingenuity, novelty away evoked a spontaneous and acute task called for. He also had the innate and imagination. They reveal a sharply sense of loss among his numerous stu- ability to spot and nurture talent. No analytical and creative mind. He was a dents, colleagues and admirers spread all wonder he was able to transform the spectroscopist in the classical mould, and over the country. It was the end of an elegantly focused on both linear and non- era, many felt; but as a teacher he had linear domains to probe the systems he kindled so many young minds and worked on. His penchant for working on shaped their destiny that his subtle influ- ‘clean’ systems and ‘precise’ measure- ence, they hoped, would live on, endur- ments naturally drew him to low- ing the test of time. temperature spectroscopy of single crys- tals doped with transition metal or rare earth (RE) ions. The man To the discerning and perceptive obser- Low-temperature single-crystal ver, Chowdhury appeared to be poised spectroscopy between two worlds – one tradition and old values, and another of pure reason During the initial days of his research ca- and rationality. The former made him the Department into a vibrant centre of ex- reer in India, Chowdhury was a full-time unmistakable aristocrat that he was; a cellence where atomic and molecular professor of chemistry in Presidency towering personality without the imperi- spectroscopy, photochemistry, photody- College, Kolkata, teaching a host of sub- ousness generally characteristic of such namics and theoretical chemistry flour- jects (thermodynamics, spectroscopy, personages. He was kind and benign and ished in all their splendour. Under his group theory, quantum mechanics) at the refused to stoop low, no matter what the able leadership of two decades and a UG and PG levels, and shared time be- provocation was. The latter helped him half, the Department reached the zenith tween his laboratory in the College and imbibe the qualities of a great scientist of its reputation both in the national and the one in the erstwhile Department of and teacher who could kindle the spirit international arena of modern physical Magnetism in IACS (now the Depart- of enquiry in young minds, encourage chemistry. Chowdhury not only believed ment of Solid State Physics), where he them to question, debate and discover the that a scientist must be able to think and spent two years as a CSIR pool officer sheer pleasure of learning. As a scientist grow freely, but also practised it with the (1964–66) after returning from USA. His he was an explorer of innovative ideas, sincerity of a true believer. The freedom focus was on low-temperature polarized who would never settle for anything that that he gave to his students, the spirit of one-photon absorption (OPA) and emis- was ambiguous, imprecise or inaccurate. enquiry that he fostered among his col- sion (OPE) spectroscopy of single crys- When Chowdhury came to head the leagues, and the lively interest that he tals of transition metal complexes like +3 Department of Physical Chemistry at always displayed in any new develop- K3Cr(CN)6, K3Mn(CN)6, Co doped in IACS in 1976, he faced a formidable ment are examples of qualities rarely met CsCdCl3, etc. Several spin-forbidden challenge – he was leaving the niche he in these days of quick results and fash- transitions in potassium chromicyanide 4 2 2 2 had carved out for himself in the famous ionable pursuits. The depth and the ( A A2, E and T1, for example) Presidency College (now Presidency breadth of expertise that the department were located and analysed in the low University), Kolkata, his alma mater, acquired during his tenure is not just a symmetry field and g value in the 2E where he became professor of chemistry testimony to his qualities, but a tribute to state was determined accurately2–5. It was at a young age of 28, and where his leg- his astute guidance which inspired clear that Chowdhury intended to blend endary teaching skill grew and attained through personal example. Chowdhury experiments with appropriate theoretical stellar heights during the ten years was a born teacher and did not give up calculations to remove any ambiguity in CURRENT SCIENCE, VOL. 113, NO. 12, 25 DECEMBER 2017 2367 PERSONAL NEWS assignments and construction of energy- Two-photon spectroscopy In circularly polarized light, however, E level diagrams of the transition metal is strongly allowed while A1 remains ions in different chemical environments. The advent of lasers opened up new ave- only weakly allowed in two-photon During this period, he succeeded in set- nues for probing the rare earth systems absorption. By comparing polarized one- ting up a pulsed magnetic field (7– by making use of nonlinear spectros- and two-photon absorption spectra of 8 tesla) generator (locally fabricated) and copy. The simplest nonlinear tool that triptycene, Chowdhury and associates integrated it with a Karl Zeiss spectro- Chowdhury and his associates exploited succeeded in locating two excited elec- graph. He leveraged the integrated sys- for fn–fn transitions was two-photon tronic states, one at 2500 cm1 above the tem to measure Zeeman splittings of absorption (TPA) spectroscopy. fn–fn other15. several transition metal and rare earth transitions are intrinsically two-photon single crystals6 at low temperatures. allowed. If the crystal was centrosym- metric, TPA would allow them to locate Jet-cooled molecular spectroscopy the phonon free ‘0–0’ bands exactly. In Spectroscopy of multichromophoric addition, the different selection and po- In the 1980s, laser-induced fluorescence organic molecules (phase I) larization rules operative for two-photon spectroscopy of molecules cooled in transitions could allow them to locate a supersonic jets grew into a powerful me- Chowdhury also started taking interest in term or its crystal field components thod of probing vibrational-level struc- the low-lying excited states of organic missed out in one photon absorption tures and intramolecular dynamics. In the molecules containing multiple chromo- (OPA) spectrum. The two-photon spectra rarefied atmosphere following expansion phores such as 2,2-pyridil, mesityl, ben- of single crystals of gadolinium-DG in a jet and the resultant cooling, the mole- zil, indantrione, alloxan, etc. Vicinal di (non-centrosymmetric)12 and Gd-elpaso- cules are not only isolated but also have and polyketones were convenient exam- lite (centrosymmetric)13 provided valu- very low vibrational and rotational tem- ples of molecules with several low-lying able information about states not seen in peratures. The state in which molecules n* states, which provided the opportu- the OPA spectrum. The initial foray into are prepared is well defined. The spec- nity to gain insight into the fine balance two-photon spectroscopy excited his trum is free of hot bands and is therefore between the ‘through-bond’ and ‘through- keen interest in polarized two-photon ab- amenable to clear assignments. Chowd- space’ interactions that shaped the dispo- sorption, wherein selection and polariza- hury’s attention was focused on the pos- sitions of these electronic states. Here tion differentials could be expected to sibility of using the jet expansion too, Chowdhury displayed his basic am- shed light on the nature of the electronic technique to probe low-frequency, highly bidextrous disposition. He deftly com- energy levels more completely. Chowd- anharmonic, large amplitude motion of bined available theoretical tools with hury turned his attention to double and nuclei and exploiting the information to polarized (one-photon) absorption and triple molecules in which two or more - construct the excited state potential emission spectroscopy to locate the elec- chromophoric units weakly interact caus- energy surfaces on which the nuclear dy- tronic states responsible for the observed ing splittings in the energy levels14. The namics took place. To achieve this objec- absorption and emission spectra7–9. double molecules and the exciton split- tive he needed a supersonic jet expansion ting displayed by them were well known. set-up, which was designed and fabri- Little was known at that time about the cated in the IACS workshop. The vacuum Spectroscopy of rare earth single splitting patterns in triple molecules like was maintained at 10–4 torr.