Mulliken, Robert Sanderson

Physicist. (1896-1986)

Chemical physicist. Born 1896. B.S., Massachusetts Institute of Technology, 1917. Ph. D., University of Chicago, 1921. Assistant professor of physics, New York University, 1926-1928. Associate professor of physics, University of Chicago, 1928-1931; professor, 1931-1956; Ernest DeWitt Burton Distinguished Service Professor, 1956-1961; Distinguished Service Professor of physics and chemistry, 1961-1985. Distinguished Research Professor of chemical physics, Florida State University, 1964-1971. Studied experimental spectroscopy, developed molecular orbital (MO) method for explaining molecular structure. Nobel prize in chemistry, 1966. Died 1986.

Robert Sanderson Mulliken was born in Newburyport, Massachusetts on June 7, 1896. His father, Samuel Mulliken, was a chemistry professor at the Massachusetts Institute of Technology, where Robert Mulliken received his B.S. degree in chemistry in 1917. During World War I, Mulliken worked under James B. Conant of the Chemical Warfare Service doing research on poison gases. He began graduate work in the Chemistry Department at the University of Chicago in 1919 under the supervision of William D. Harkins. He received a National Research Fellowship upon completing his Ph.D. degree in 1921 with a thesis on the partial separation of mercury isotopes by evaporation. Mulliken continued this research at the University of Chicago until 1923, when he went to Harvard University to learn spectroscopy and to study theoretical physics. Visiting Europe in the summers of 1925 and 1927, he met many of the most important physicists of the day including Niels Bohr and Erwin Schrödinger, along with a number of younger scientists. He returned to Europe as a Guggenheim Fellow in 1930 and again in 1932-1933, accompanied by his wife, Mary Helen Von No‚ Mulliken, whom he married on December 24, 1929. The Mullikens had two daughters, Lucia Maria born in 1934, and Valerie No‚ born in 1948.

Mulliken joined the faculty of New York University as an assistant professor of physics in 1926 and remained there until 1928, when he returned to the University of Chicago as Associate Professor of Physics. He was made Professor of Physics in 1931, and Ernest DeWitt Burton Distinguished Service Professor of Physics in 1956. He remained an active member of the faculty after official retirement as Distinguished Service Professor of Physics and Chemistry from 1961 through 1985. He also held an appointment as Distinguished Research Professor of Chemical Physics during winter quarters at Florida State University in Tallahassee from 1964-1971. Mulliken died in Alexandria, Virginia on October 31, 1986.

Mulliken’s postdoctoral work at Harvard led him to explore the relations between molecules and atomic electronic states through analysis and classification of band spectra. Following the establishment of the new quantum theory in the 1920s, Mulliken (contemporaneously with Friedrich Hund) applied group theoretical methods to these phenomena and developed the molecular orbital, or MO, method for explaining molecular structure. At the same time, he continued the work in experimental spectroscopy he began at Harvard and was instrumental in the design and construction of a spectroscopic laboratory at the University of Chicago. This extensive theoretical and experimental work in the study of molecules was highlighted in the 1930s with the publication of a series of papers on electronic structures of Polyatomic Molecules and valence. It was this foundational work that is largely credited for his receipt of the Nobel Prize in chemistry in 1966. Mulliken followed this work in the late 1930s by extending the MO theory to the study of the absolute strengths of electronic transitions in molecules.

The MO theory was one of two descriptive theories developed in this period to apply the ideas and formalisms of quantum mechanics to the problems of molecular structure. While the valence bond theory (articulated primarily by Heitler, London, and Pauling) treated molecules as made of interacting but individual atoms, each maintaining its own electrons, the MO theory as developed by Mulliken and others treats the electrons of a molecule as being spread out in wave functions, or orbitals, over all the atoms in a chemical bond of molecule. This model gave predictive equations describing properties of spatial structure, chemical binding energies, ionization potentials, and molecular spectra.

While Mulliken’s early work provided the MO theory with a rigorous mathematical form, the complexity of the equations makes their exact solution impossible. Attempts were made during the 1940s and 1950s to improve available approximations through the use of semi empirical methods, and beginning in the late 1940s, Mulliken and his collaborators were engaged in research using new wholly theoretical techniques and increasingly sophisticated computers to improve the accuracy of calculations based on the MO theory. During the 1950s and 1960s, he pursued research on the study of donor-acceptor relations and charge-transfer complexes, conjugation and hyper conjugation in ions, and population analysis on LCAO-MO wave functions.

During World War II, Mulliken served as Director of the Information Division of the Plutonium Project at the Metallurgical Laboratory of the University of Chicago. In 1944, he helped to draft the Plutonium Project’s first “Prospectus on Nucleonics” on peaceful uses of atomic energy. Following the war, Mulliken’s active research group in spectroscopy resumed its activities, and from 1952 were officially designated the Laboratory of Molecular Structure and Spectra. Dozens of researchers from all over the world, both theoreticians and experimentalists, spent time at LMSS as students, postdoctoral fellows, or research associates. Mulliken spent a year in Oxford as a Fullbright Fellow in 1953, and served as scientific attach‚ at the United States Embassy in London during 1955. He maintained extensive contacts with scientists throughout Europe, India, and Japan and attended many international scientific meetings.

In the course of his career, Mulliken published over 200 papers. In addition, he collaborated on the publication of three review volumes in the 1960s and 1970s. His autobiography, Life of a Scientist, was edited by Bernard Ransil and published posthumously by Springer-Verlag in 1989.

Mulliken received many honorary degrees and most of his profession’s highest honors, including the G. N. Lewis Medal, the Peter Debye Award, the J. Willard Gibbs Medal, and the Priestley Medal of the American Chemical Society. He was awarded the Nobel Prize in Chemistry in 1966. He was a member of many scientific societies both in the U.S. and abroad, including the National Academy of Sciences to which he was elected in 1936. A member of the American Physical Society from the 1920s, he was in 1944-1945 chairman of a committee to organize a Division of Spectroscopy. Their work led to the establishment of the Division of Chemical Physics, with Mulliken as its inaugural chairman, in 1951.

Robert Sanderson Mulliken, Nobel Prize-winning physicist and chemist, was born in Newburyport, Massachusetts on June 7, 1896. He earned a B.Sc. degree from the Massachusetts Institute of Technology in 1917, and a Ph.D. from University of Chicago in 1921. He served on the faculty of New York University's physics department for a short time, before returning to the University of Chicago in 1928. He served as a professor of physics and chemistry for over 50 years. His foundational research on chemical bonds and the electronic structure of molecules led to his 1966 Nobel Prize in chemistry.

For a detailed biographical summary, see the finding aid for the Robert S. Mulliken Papers.