Catalán, Miguel Antonio

(b. Zaragoza, Spain, 9 October 1894; d. Madrid, Spain, 11 November 1957),

experimental spectroscopy.

Catalán entered the University of Zaragoza in 1908, at the age of fourteen; from there he went to the University of Madrid, where he completed his studies with a D. Sc. under A. Del Campo. He then joined the Laboratorio de Investigaciones Fisicas in Madrid, where he worked mainly on atomic spectroscopy, a field that had attracted him from his student days and to which he devoted the major part of his creative efforts for the next forty years.

A Spanish government fellowship enabled Catalán to spend the year 1920/1921 in Alfred Fowler’s laboratory at Imperial College, London, then a leading center of atomic spectroscopy outside of Germany and the Netherlands. This field, which for many years had looked upon spectra as no more than the language of atoms, was slowly moving into the very center of physical research, spurred by the Bohr atomic model, which provided an interpretation of that language.

On the experimental side, spectroscopic studies up to 1922 had revealed the following important features:

1. The spectra of most elements, especially of the first three groups of the periodic table, are made up of distinct lines that could be classified into at least four different series, which are known as the sharp (s), principal (p), diffuse (d), and fundamental (f)series.

2. Each line was known to be made up of one, two, or three closely spaced lines. These were referred to as singlets, doublets and triplets, respectively. The physical origin of these was still obscure.

3. In general the alkali metals, such as sodium and potassium, gave rise to doublets, and the frequency difference was almost the same in all the sharp and diffuse series. In the second group of the periodic table, which consists of the alkaline earth metals, many of the lines are actually triplets, although singlets are also present. These characteristics refer to arc spectra, or spectra from neutral atoms. In the case of spark spectra, or spectra of ionized atoms, the elements behaved as if they belonged to the next group, in accordance with the so-called displacement law.¹

From these facts one could tabulate the nature of complex spectra, as follows:²

Manganese belongs to group VII in the periodic table, and from the pattern observed, its spectrum should be made up of doublets. Triplets had, however, been detected in the manganese spectrum.

It must be realized that the spectra of heavier elements are very complex and had not been fully resolved into their components at that time. But since at least some of these lines could be arranged into series, it was generally surmised that all complex spectra could eventually be resolved into doublets and triplet-singlets.

Catalán felt that the investigation of a spectrum characterized by multitudinous lines could reveal more general regularities that in turn would probably account for the recalcitrant lines in the first two columns of the periodic table as well as for the complex spectra in the center. He therefore undertook a detailed study of the manganese spectrum in Fowler’s laboratory.³

Catalán’s extensive studies of the manganese spectrum revealed in it a system of four triplets that were analogous to the ones found in the alkaline earth spectra. He also found a system of three narrower triplet series that were of the sharp, diffuse, and principal types and corresponded to the singlet system of the alkaline earths. And finally there was yet another, still narrower system of triplets that was parallel to the preceding ones.

Each diffuse triplet in the manganese spectrum was actually analyzed into nine lines. Catalán explained this situation, which he described as multiplets, by assuming the d terms to be fivefold, thus departing from the accepted views about the structure of atomic spectra.

While he was back in Spain, Catalán made similar studies of chromium, selenium, molybdenum, and other elements, and showed that the phenomenon observed in manganese was not restricted to that element but, rather, was a general regularity.

Arnold Sommerfeld, a leading theorist in the field, met Catalán during a visit to Spain in April 1922. Impressed by Catalán’s discovery, he took back to Germany the manuscript of Catalán’s epochal paper, which appeared the following year in the Philosophical Transactions.⁴ He then showed that his “inner” (total angular momentum) quantum numbers could be assigned to Catalán’s multiplet terms.⁵ Very soon thereafter both theoreticians and experimentalists began to investigate multiplets with great enthusiasm and success, for they now had the key for unraveling the spectra of the elements in the center of the periodic table. The intense interest in this field during the period 1923–1925 was due especially to the lack of an adequate explanation of the physical origin of multiplets, indeed even of doublets and triplets. It was widely anticipated that the investigation of this problem would lead to the uncovering of the quantum mechanics of the atom. These researches did contribute to establishing the structure of the atom, but the actual explanation of the multiplets are found to lie in the spin of the electron, and quantum mechanics emerged from a different line of research.

Sponsored by Sommerfeld, Catalán received an International Education Board (Rockefeller Foundation) fellowship to work with Sommerfeld at Munich during the year 1924/1925. Here, along with Karl Bechert, Catalán analyzed several other spectra; and when he returned to Madrid in the fall of 1925, Bechert followed him with an I. E. B. fellowship. Thus Catalán maintained a close cooperation with the Munich school of theoretical spectroscopy.

In 1930 Catalán became the chief of the section on atomic spectroscopy of the Rockefeller Institute in Madrid. He won the admiration and affection of the many students under his direction, for besides his abilities as a scientist, Catalán was an extremely cordial person and a gifted teacher—indeed he often considered himself a teacher first. Realizing the importance of maintaining bridges between the scientist’s world and that of the layman, he often gave popular lectures on science to nontechnical audiences.

Catalán’s numerous scientific papers firmly established his reputation on the international scene. After World War II he visited the United States a number of times, lecturing and working in various centers. In 1950 he was made head of the department of spectroscopy at the Institute of Optics in Madrid. Two years later he became a member of the Joint Commission for Spectroscopy of the International Council of Scientific Unions. In 1955 he was elected to the Royal Academy of Sciences in Spain. He also made a number of lecture tours in Latin America.

Catalán was active until his last year. His death, not long after his sixty-third birthday, was sudden.

NOTES

1. Arnold Sommerfeld. Atombau and Spektrallinien, 3rd ed.(Brunswick, 1922), pp. 266–471.

2. F. D. Foote and F. L. Mohler, The Origin of Spectra (New York,1922), p. 42.

3. The earliest studies on the manganese spectrum had been made by Sir William Huggins in 1864.

4. Catalán, “Series and Other Regularities in the Spectrum of Manganese,” in Philosophical Transactions of the Royal Society, 223 (1923), 127–173.

5. Arnold Sommerfeld, “Uber die Deulung verwickelter Spektren,” in Annalen der Physik, 70 (1922), 32–62.

BIBLIOGRAPHY

A bibliography of Catalán’s works is in Poggendorff, VI, pt. 1 (1936), 413; and VIIb, pt. 2 (1967), 742–743. Letters relating to Catalán’s work are listed in T. S. Kuhn et al., Sources for History of Quantum Physics. An Inventory and Report (Philadelphia, 1967), 28b, l20b, 130c, 135a.

There is an article on Catalán in Enciclopedia universal ilustrado europeo americana (Bilbao, 1931), app., pp. 1266–1267, and ann. supp. for 1957–1958 (1961), pp. 199–200. Obituaries are Journal of the Optical Society of America, 48 (1958), 138; R. Velasco et al., in Anales de la R. Sociedad española de fisica y quimica, ser. A, 53 (1957), 217, repr. in ser. B (1957), 773; and R. Velasco, in Nature, 181 (1958), 234.

Varadaraja V. Raman