Organizer, Presiding: Ronald K. Smeltzer
Spectroscopy and the quantum revolution: Old quantum theory gives way to quantum mechanics / Kenneth R. Metz
Most chemists are aware of the dynamic historical interplay between the evolution of spectroscopic theory and the development of quantum theory in the early part of the twentieth century. Beginning with Bohr's 1913 planetary model of the atom, spectra provided the ultimate proving ground for new ideas in quantum theory, culminating in the matrix / wave mechanics revolution of the mid-1920's. Two pivotal monographs provide snapshots of the state of theoretical development in spectroscopy as old quantum theory evolved into quantum mechanics. The first is Arnold Sommerfeld's 1919 Atombau und Spektrallinien (English edition, 1923), a masterful exposition of the modified Bohr model, or old quantum theory, at its zenith. The second is that of Ruark and Urey (Atoms, Molecules and Quanta, 1930), which incorporated results from the new wave mechanics and signaled the arrival of an enormously successful era in spectroscopy. This presentation will compare and contrast these treatments
Spectroscopy and the periodic table: Tribute to Friedrich Hund's Linienspektren und periodisches System der Elemente / William Barry Jensen
Following J. J. Thomson's proposal of his famous "plum pudding" model of the atom in 1904, over two decades would pass, during which numerous chemists and physicists proposed various electronic configurations for the elements, before we arrived at our current s,p,d,f configurations, as first presented by Friedrich Hund in his classic 1927 monograph Linienspektren und periodisches System der Elemente. The talk will outline these various proposals as well as the path by which Hund's final configurations made their way into the textbook literature.
Gerhard Herzberg: Physicist, chemist and astronomer / Donald C. Morton
Herzberg began his career studying at the Technische Hochschule in Darmstadt, Germany. Following postdoctoral appointments at Göttingen and Bristol, he returned to Darmstadt. However, life under the Nazi authorities became more and more difficult because his wife, Luise, was Jewish. Consequently, in 1936, he accepted a position at the University of Saskatchewan in Canada. There, with Alex Douglas, he showed that CH+ was the origin of three unidentified interstellar absorption lines. Herzberg also completed both German and English editions of Atomic Spectra and Atomic Structure and Spectra of Diatomic Molecules with translations by John Spinks. In 1945 he moved to the Yerkes Observatory of the University of Chicago, where he measured the quadrupole lines of H2 in an absorption cell. He returned to Canada in 1948 to the National Research Council in Ottawa. There his research included free radicals, which were mentioned specifically in his 1971 Nobel Prize citation
Raising the bar for those who followed: Henry Rowland and the solar spectrum / Steven C. Turner
No consideration of twentieth century spectroscopy can be complete without recognizing the contributions of Henry Augustus Rowland. In particular, his Photographic Map of the Normal Solar Spectrum, 1888, and Preliminary Table of Solar Spectrum Wave-Lengths, 1898, provided the foundations on which future developments in spectroscopy would be built. Like any true landmarks, these works are important on a number of historic levels. In their most obvious role, as laboratory standards, they represented a new level of precision measurement and created a global demand for diffraction gratings made on Rowland's machines. Yet Rowland's successes also inspired efforts to exceed him and pushed American spectroscopy to new levels of precision. Ultimately we can gauge Rowland's importance by the fact that contemporary wavelength tables continue to be called “revisions” or “extensions” of his work.
A brief history of light scattering spectroscopy / Gary D. Patterson
One of the most identifiable phenomena in our world is the blue of the sky. The differential light scattering as a function of wavelength was explained by Lord Rayleigh in terms of Maxwell's equations for the interaction of light with polarizable atoms or molecules. The elementary theory predicted perfectly polarized light when the sun was near the horizon and the sky was observed overhead, but actual scattered light from the atmosphere is depolarized. Rayleigh successfully explained this phenomenon in terms of anisotropically polarizable molecules in the atmosphere (nitrogen and oxygen). When monochromatic light is scattered, its color changes due to many effects. The scattering atoms or molecules are moving and the scattered light energy is changed due to energy exchange. The simplest phenomenon is the Doppler effect due to the translational motion of the scattering particles. The observed light scattering spectrum for a monatomic gas at low pressure reflects the Maxwell-Boltzmann distribution of particles velocities. At higher pressures, the light scattering spectrum is more complicated and reflects cooperative behavior on length scales longer than the mean free path of the particles. This spectrum was predicted by Landau and Plazcek. Light is also scattered by all liquids and solids. Brillouin predicted that thermal sound waves in liquids and solids would scatter light and this effect was eventually observed. Raman predicted that vibrational and rotational motion in molecules would lead to energy exchange during light scattering and received the Nobel Prize for his insight. A fully quantum theory of light scattering was developed by Plazcek and Teller.
Vibrational and vibration-rotational molecular spectroscopy 1900-1960 / Alfons Weber
The development of vibration and vibration-rotation molecular spectroscopy over the period from 1900 to 1960 will be reviewed. Emphasis will be given to the role played by instrumentation and some of the personalities, as well as books of historical, biographical, and current importance that played a significant role in the development of this field of study. Many of the working ideas that were found to be successful in the era of the old quantum theory were verified or slightly modified by subsequent quantum mechanical insights. These allowed the extension of knowledge accumulated for diatomic molecules to polyatomic systems, especially after the discovery of the Raman effect and the introduction of symmetry arguments in the analysis of observed spectra. The shift from physics to chemistry due the development of “user-friendly” spectrometers and the introduction of the FG-matrix technique for normal coordinate calculations will be addressed. The contributions made by several prominent women spectroscopists will be highlighted.
Chemistry of the stars: Scheiner & Frost's treatise on astronomical spectroscopy / Ronald S. Brashear
Although not technically printed in the twentieth century, Julius Scheiner's Die spectralanalyse der gestirne had a tremendous impact on all astrophysicists in the early years of the century. Its importance grew tremendously when Edwin B. Frost translated, revised, and enlarged it four years later as A treatise on astronomical spectroscopy. Scheiner's mentor, H. C. Vogel, had considered writing a book to consolidate the prevailing knowledge of astronomical spectroscopy but as his health failed he charged his young assistant to write the first major treatise on the subject. Scheiner's work appeared in 1890 and was an instant success with younger astronomers who were hungry for just such a book. Frost's translation in 1894 spread Scheiner's work to an even larger audience in the United States, where men like George Ellery Hale would make the country the center of observational astrophysics for the first half of the twentieth century.
Two classics of early American solar spectroscopy / Richard L. Kremer
Charles A. Young, professor of natural philosophy and astronomy at Dartmouth College from 1866-77, became one of America's first internationally acclaimed astrophysicists by virtue of two classics—an instrument and a book. His multi-prism, double-pass spectroscope, built by Alvin Clark & Sons, exposed the technical limit of attempts to increase dispersion by adding prisms, a limit reached just as Rowland's gratings became available. Young's book on the Sun, however, joined a successful trend, published in the International Scientific Series. These wildly popular books began appearing in London in the 1870s; by the 1880s American editions were being printed by D. Appleton & Company in New York. Through these books, authors such as Darwin, Spencer, Tyndall, Lockyer, Wurtz, Marey, etc. popularized the late nineteenth-century sciences ... and Young became known as America's premier solar physicist.