Rayleigh, Ramsay, Rutherford and Raman – their connections with, and contributions to, the discovery of the Raman effect

Abstract

The key contributions of the four great Nobel Laureates – Lord Rayleigh, Sir William Ramsay, Lord Rutherford and Sir Chandrasekhara Raman – to the understanding of light scattering, to the identification and classification of the rare gases, and to the discovery in 1928 of the Raman effect are outlined. The interactions between these scientists are explored, in particular those of Rayleigh with Ramsay (in establishing the physics and chemistry of the rare gases), Ramsay with Rutherford (on studies of the radioactivity of radium dibromide and on the discovery of radon and its position in the periodic table), and Rutherford with Raman (in supporting Raman's career via the Royal Society and as a nominee for the Nobel Prize). The resilience and dedication of these scientific pioneers is emphasised, noting in particular that Rutherford and Raman emerged with success from unlikely backgrounds and from countries far removed from the then centres of scientific excellence. Key developments from 1928 onwards in the light sources used for the excitation of Raman spectra and in the detectors of Raman scattered radiation are outlined. Attention is drawn to the mounting number of scientific areas which continue to be opened up by Raman microscopy and many other derived techniques such as SERS, TERS, etc.

Introduction

The ways in which science develops through chance happenings and meetings is endlessly fascinating and always will be. The present article illustrates how pairwise meetings between four scientists, roughly 15 years apart in their respective careers, led to the discovery by C. V. Raman of an effect in light scattering, the consequences of which and capabilities of which are still expanding enormously. The article centres on the key contributions of the four great Nobel Laureates – Lord Rayleigh, Sir William Ramsay, Lord Rutherford and Sir Chandrasekhara Raman – to the understanding of light scattering, to the identification and classification of the rare gases, and to the discovery in 1928 of the Raman effect.

Subsequent technical developments have demonstrated the capability of the technique to clarify many aspects of inorganic, organic and physical chemistry, structure and reactivity in all states of matter, materials science, and now aspects of medical science. The relevant discoveries of the four players are discussed chronologically, beginning with Lord Rayleigh.

Lord Rayleigh

John William Strutt was born in Langford Grove, Maldon, Essex in 1842, and attended Harrow School before entering Trinity College Cambridge in 1861 to study mathematics. He graduated BA (senior wrangler) in 1865, MA in 1868. He was undoubtedly a brilliant mathematician and physicist, top of his year at Cambridge, as recognized by his subsequent election to a Fellowship of Trinity College. His discovery of the basis of light scattering was made in 1870, three years before he succeeded to the Barony of Rayleigh on the death of his father in 1873. He became the second Cavendish professor of physics at Cambridge (following on from James Clerk Maxwell) from 1879 to 1884, during which period he studied the dynamic soaring of seabirds. From 1887 until 1905 he was Professor of Natural Philosophy at the Royal Institution (RI) in London, succeeding John Tyndall who had studied the scattering of light by dust particles and colloids. Rayleigh (Fig. 1 and 2) was a classic gentleman physicist, mainly remembered for his development of the theory of human sound localization and for his research in a host of other areas covering almost the whole of physics. This included the development of the theory of light scattering by molecules (which are much smaller than the wavelength of the light used), giving rise to the term Rayleigh scattering and to the explanation as to why the sky is blue (based upon the fourth power frequency dependence of the intensity of light scattering). His research in sound, light scattering, etc., was profound and, had the Nobel Prize existed in the late 1800s, he must surely have been a serious candidate for it at that time.

Fig. 1 Lord Rayleigh (Portrait of John William Strutt, © The Royal Society).

Rayleigh's contribution to the discovery of the element argon in the atmosphere was the critical discovery which led to his being awarded the Nobel Prize for Physics in 1904. The development some 60 years later of rare gas lasers was an unexpected bonus from his research, as lasers became crucially important as monochromatic light sources for Raman spectroscopy and a host of other applications. Key features of his career are given in Table 1 along with those of the three other Nobel Laureates to be discussed.

Table 1 Rayleigh, Ramsay, Rutherford and Raman: all FRS, all Nobel Laureates and all Honoured

Scientist	Born/died	FRS	Nobel Laureate	Subject	Honour
Rayleigh	1842–1919	1873	1904	Physics	Lord
Ramsay	1852–1916	1888	1904	Chemistry	KCB
Rutherford	1871–1937	1903	1908	Chemistry	Lord
Raman	1888–1970	1908	1930	Physics	Kt

Rayleigh was awarded many of the highest distinctions from scientific bodies throughout the world, including the Rumford, Royal and Copley medals of the Royal Society, for the quality and depth of his research discoveries.

Sir William Ramsay

William Ramsay was born in Glasgow in 1852, coming from a very educated Scottish family who instilled in him an interest in both science and language. Indeed he developed a flair for learning languages quickly, in particular German. He attended the Glasgow Academy and then the University of Glasgow before moving to Tubingen to carry out research on toluic and nitrotoluic acids under Fittig for a PhD, graduating in 1872. He was then appointed Assistant to the professor at Anderson College Glasgow, a position which he held until 1879 when he was appointed to the chair of chemistry at Bristol. Later, in 1887, he succeeded Alexander Williamson at University College London (UCL), becoming Professor of Inorganic and General Chemistry (Fig. 2 and 3). It was here that his most notable discoveries were made.¹

Fig. 2 Lord Rayleigh and Sir William Ramsay (© UCL, UK).

Fig. 3 Sir William Ramsay (© UCL, UK).

In 1894 Rayleigh had noticed, by removal of the other known components of the air, a discrepancy between the density of nitrogen made by chemical synthesis and that, slightly greater, of nitrogen isolated from the air. With Rayleigh's consent, Ramsay began work on this problem and by August of that year, Ramsay announced that he had isolated from air a heavy component, previously unknown, which did not appear to have any chemical reactivity. He named this gas argon.

In 1895 Ramsay isolated a gaseous constituent from certain minerals, notably the uranium ore cleveite; it transpired that this gas gave the identical emission spectrum to that previously identified by Jules Janssen in the sun's corona during a total eclipse observed in 1868 in Guntur, India. The gas, not previously detected on Earth, was given the name helium (Gk. helios, sun) by Norman Lockyer and Edward Frankland (both London scientists) and recognised to be another member of the new group of rare gases. Working with Morris Travers, Ramsay then went on to discover neon, krypton and xenon in 1898 in the air. Ramsay received the Nobel Prize for Chemistry in 1904 for discovering the rare gases on earth and in the air and for determining their place in the periodic table. Radon was first made by Rutherford and Soddy in 1899. However it was not shown until 1910, and then by Ramsay and Whytlaw-Gray, that this element is also a member – the densest – of the new periodic group of rare gases. It was a great honour for me to have been appointed in 1989 to the inaugural Chair of Chemistry in Ramsay's name at UCL, where memorabilia relating to his career are on display in the foyer of its Department of Chemistry.

Rayleigh and Ramsay (at the RI and UCL, respectively) were well known to each other and the institutions in which their key work was undertaken remain very closely linked even to this day.

Ramsay and his wife toured India for two and a half months in 1900 at the invitation of the Tata family in order that he could give advice regarding the setting up of the Indian Institute of Science (IIS). His recommendation to the Tata Committee was that it be sited in Bangalore. Moreover it was on Ramsay's recommendation that one of his own collaborators at UCL, Morris Travers, was appointed in 1906 to be the first Director of the IIS, as commemorated in the plaque on the front of the Institute building. Significantly both the 6th (in September 1978) and the 23rd (in August 2012) International Conferences on Raman Spectroscopy (ICORS VI and XXIII) were staged in Bangalore, the latter actually in the IIS itself.

Lord Rutherford

The early life of Ernest Rutherford was remarkable and could not have been more different from that of either Rayleigh or Ramsay. He was born and grew up in the 1870s in a very small settlement of Spring Grove, now Brightwater, in the Nelson province of the South Island of New Zealand. He was very much a country boy, keen on exploring the local countryside. His family moved in 1883 to the small township of Havelock in the adjacent province of Marlborough, where he attended the local very small school until 1886 (curiously also attended, much later, by William Pickering, who went on successively to Wellington College, Canterbury College and then Caltech, graduating PhD in 1936, and eventually becoming Director of the Jet Propulsion Laboratory in Pasadena over the period 1954–1976).

Marlborough province had no secondary school before 1900,^2,3 and it was only by hard work and several strokes of good luck that Rutherford won scholarships first to Nelson College (1887–1889) and then in 1890 to Canterbury College (in Christchurch) of the University of New Zealand. There he completed a BA in 1892 and an MA in 1893 with first-class honours in mathematics and mathematical physics, as well as first class honours in physical sciences. Also in 1893 he carried out his first original research on the high frequency magnetisation of iron. In 1894 he completed a BSc degree in chemistry and geology and also undertook research leading to his first scientific publication. Seeking an opportunity to carry out further research abroad, Rutherford then applied for the only scholarship then available for a New Zealander to travel and be supported abroad, the newly founded biennial 1851 Exhibition Scholarship. However although his thesis was judged to be excellent, he came second to James Maclaurin, a chemist from Auckland, who had developed the cyanide process for the extraction of gold from mineral ores. Fortunately for Rutherford, by the time the announcement was made, Maclaurin had both got married and taken permanent employment as a New Zealand government analyst (later becoming Dominium Analyst), with the consequence that he withdrew his candidacy. Maclaurin's younger brother Richard, an excellent mathematician, went on to become the President of the Massachusetts Institute of Technology in Boston.

The way thus opened up for Rutherford to be offered and to accept the 1851 Exhibition and therewith to travel in July 1895 to the UK to undertake research with J. J. Thomson in the Cavendish Laboratories at Cambridge. This was the first year in which non-Cambridge graduates had been admitted into the Cambridge research school. Rutherford took full advantage of this move and by 1898 he had obtained a BA (Research) – Cambridge had not at that stage introduced the PhD degree – and he had carried out research in six major areas of physics – magnetic properties of iron at high frequencies, the dielectric properties of materials, the detection of electric waves, electrical conduction in gases, and the nature of X-rays and radioactivity.

Recognition followed fast, and Rutherford was appointed Macdonald professor of physics at McGill University in Montreal in 1898. New discoveries abounded, e.g. alpha and beta particles in 1898, the principle of the smoke detector in 1899, radon in 1899, the reconciliation of determinations of the age of the earth by physicists and geologists in 1905, etc. He received a DSc degree from the University of New Zealand in 1901, was elected a Fellow of the Royal Society in 1903 and appointed Langworthy professor at Manchester in 1907. He was awarded the Nobel Prize in Chemistry in 1908, his citation stating that this was for “investigations into the disintegration of the elements and the chemistry of radioactive substances”. He was appointed to Thomson's chair in the Cavendish Laboratory in Cambridge in 1919, and went on to become President of the Royal Society 1925–1930 (Fig. 4) and to be appointed to the Order of Merit (OM) in 1925.

Fig. 4 Lord Rutherford (© The Royal Society).

Rutherford showed great strength of character and resilience in overcoming the many serious difficulties associated with starting his career so far from the centres of knowledge and research. He travelled considerably and hosted many international figures in Cambridge. His 36 medals from Societies around the world are on display at the University of Canterbury in Christchurch and testify to the brilliance of his discoveries. He knew Raman and did much to help him in his career, as will be evident in the next section.

Sir Chandrasekhara Raman

Although Raman had his own difficulties to overcome, they were different from Rutherford's. C. V. Raman was born near Trichinopoly in southern India in 1888. When he was 4 years old, his father was appointed a lecturer in physics at Mrs A. V. Narasimha Rao College in Vizagapatam (known colloquially as Vizag), a port on the eastern seaboard of India, north of Madras. The family had a real interest in education and this helped Raman's scholastic background and so enabled him to gain entry to Presidency College, Madras.^4–6 He graduated BA in 1904 and MA(I) with record marks in 1907, coming first in the class when only 19 years old. His teachers recommended that he should go to England for further studies but the Civil Surgeon of Madras ruled this out, considering that the young and frail Raman would not be able to withstand the rigours of the English winters. Although he wanted to enter academia, he thus applied instead to the Indian Financial Department, gaining first place in their entrance examination in February 1907. He accepted the position of Assistant Accountant General in Calcutta in June 1907 and remained in post for 10 years. Remarkably, Raman retained a great desire to continue with research and, to this end, approached the secretary of the nearby Indian Association for the Cultivation of Science (IACS) shortly after his arrival in Calcutta to enquire as to whether he could carry out research there out of hours and without pay. This request was granted. The IACS had been modelled on the Royal Institution (RI) in London and, although in operation for 30 years, it had not succeeded in having any original research published during that entire period. Raman changed this: working essentially alone and out of hours, he produced 27 original publications over the next decade, sufficient to make him fairly well known and respected internationally. Raman was then offered the newly founded Palit chair of physics in the University of Calcutta, albeit at a much lower salary (barely half!) than that which he was receiving at the tax office. The offer was accepted and he left government service. However he managed to retain most of his on-going research at the IACS and, in 1919, became its Honorary Secretary – the counterpart position to that which I held myself from 1998 to 2004 at the RI in London.

Raman began a series of visits to overseas countries and international congresses. At UCL he met William Bragg and A. W. Porter, carrying out research with the latter on conical refraction in biaxial crystals and on smoky quartz. Encouraged by Porter he also investigated with G. A. Sutherland the acoustics of the Whispering Galleries at St. Paul's Cathedral, London, showing that, as the observer moved along a dome radius, he could hear repeated waxing and waning of any sound. Raman also heard Rutherford lecture at the RI.

Raman also became interested in light scattering in the early 1920s and showed that the blue colour of the sea is not only due to reflection of the sky (as originally proposed by Rayleigh) but also to light scattering by the water molecules of the sea. He clearly had by this time made his mark on the European scene, and was elected FRS in 1924; Porter was one of his nominees.

Raman's key papers in Nature in 1928 revealed the nature of what is now referred to as the Raman effect – the scattering of light by molecules at frequencies other than that of the incident light beam.⁷ This phenomenon had been predicted by Smekal in 1923⁸ and the theory developed by Kramers and Heisenberg in 1925,⁹ but it was Raman who made the key experimental discovery, closely followed by similar studies of quartz crystals by Landsberg and Mandelstam in Russia.¹⁰ Raman and many others quickly realised that he had made a momentous discovery, as witnessed by the rapidity with which the appropriate spectroscopic equipment was set up all over the world and the realization that the scattering from molecules of all types and in all states of matter could reveal intimate details of molecular structure and bonding. He was awarded the Nobel Prize in Physics in 1930, his citation stating that the award was for “his work on the scattering of light and for the discovery of the effect named after him”. Ten physicists nominated him for the Nobel Prize in 1930, of whom Rutherford was one.

Rutherford, as president of the Royal Society (1925–1930), also presented Raman (Fig. 5) with the Hughes Medal (given for an original discovery in the physical sciences) in 1930, declaring that “The Raman effect must rank among the best 3 or 4 discoveries in experimental physics in the last decade. It has proved and will prove [to be] an instrument of great power in the study of the theory of solids”. Only two years later, in 1932, Rutherford again assisted Raman by successfully recommending that he be appointed Director of the IIS in Bangalore, a position from which he did not retire until 1948. After that he established the Raman Research Institute in Bangalore, close to the IIS, where he continued to work until his death in 1970.

Fig. 5 Sir Chandrasekhara Raman.

Development of the subject

Raman spectroscopy developed rapidly after 1928, with many expert experimentalists and theoreticians becoming absorbed with its study. Raman's original observations involved the use of sunlight as source and the eye as detector of scattered radiation – the simplest of arrangements, available to anyone, anywhere. He recognized immediately the need for a monochromatic excitation source in order to establish the exact frequencies scattered by different molecules and a photographic plate as detector. Raman's instrument was very slow, taking in the case of some gases up to a day's exposure per spectrum, but nevertheless it clearly demonstrated the effect. Subsequent technical advances were partly to do with improvements in the power density of the exciting line used (mercury arc, gas or solid-state laser), the choice of wavelength, and the nature of the detector (photographic plate, photomultiplier, charge-coupled device), each advance increasing the sensitivity of the instrumentation by one or more orders of magnitude. At UCL we recall the pioneering Raman study in 1936 on the structure of benzene by C. K. Ingold et al.¹¹ This combined one of the first applications of Raman spectroscopy with the method of isotopic substitution of hydrogen by deuterium (itself discovered only 5 years previously) to the elucidation of polyatomic molecular structures. Later, with D. J. Millen in 1946, he identified spectroscopically the nitronium ion (NO₂⁺) in nitrating mixtures, leading to the complete understanding of the mechanism of nitration; the ion was shown to be linear and centrosymmetric.¹² My own interests, originally in coordination and transition metal chemistry, moved somewhat in the late 1960s to include infrared, Raman, and resonance Raman spectroscopy, and structural studies of inorganic molecules, mixed-valence compounds and materials in all states of matter.^13–15 This whole area became of great international interest, and formed the basis of innumerable national and international conferences.

With the development of Raman microscope systems, the opportunity opened up for the compilation of Raman spectra of pigments and dyes, and hence the study and possible authentication (or otherwise) of artwork and archaeological artefacts.^16–22 This has developed into a large, growing and effective field in which Science, perhaps unexpectedly, has impinged powerfully upon the Arts. Many highly valuable illuminated bibles, manuscripts, paintings and icons have been examined in order to identify the pigments present. Raman microscopy has thus become the badly needed critical probe for forgeries, providing information which should influence auction houses immensely. Many other fields have also proved to be amenable to Raman studies and will continue to grow, viz. the study of surface phenomena, nanoparticles, new inorganic materials, semiconductors, superconductor charge-transfer salts, forensics, pharmaceuticals, biological cells and tissues, the endoscopic and intra-operative diagnosis of cancer, minerals, archaeological and planetary sites, etc. Other studies now involve more specialist techniques such as surface-enhanced Raman spectroscopy (SERS, particularly effective for the identification of dyes),^23,24 femtosecond stimulated Raman spectroscopy, tip-enhanced Raman spectroscopy (TERS), spatially offset Raman spectroscopy (SORS), X-ray Raman spectroscopy (RIXS).

Acknowledgements

The author is most grateful to Renishaw plc for financial support.

References

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Footnote

† Based upon the Inaugural Keynote Lecture (“The Four Rs Lecture: Rayleigh, Ramsay, Rutherford and Raman – where it all began”) given in the J. N. Tata auditorium at the biennial International Conference on Raman Spectroscopy, ICORS XXIII, in Bangalore, India, on 7 August 2012.

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