Robert S. Mulliken

"The Quantum Theory of Molecular Electronic Structure" (Benjamin, 1963). "Molecular Complexes. A Lecture and Reprint Volume" (John Wiley and Sons, Inc., 1969).

He has been deeply interested in valence theory and molecular structure. His earlier work on isotopes and on diatomic band spectra was followed by theoretical systematization of the electronic states of molecules, mainly in terms of the idea of molecular orbitals. This included work one electronegativities, dipole moments, and valence-state energies. A subsequent series of papers on the theoretical interpretation of absolute intensities of electronic spectra led him to computations on conjugated organic molecules, and to the quantum mechanical statement of the concept of hyperconjugation. There followed work on quantum-mechanical questions underlying molecular orbital theory and on the use of interatomic overlap integrals es measures of bond energies. His more recent work has dealt extensively with the structure and spectra of molecular complexes, on the one hand, and on the other hand (extending and developing earlier work) with the structure and spectra of the hydrogen, helium, nitrogen, and other small molecules. Most recently he has made several machine computations on diatomic molecules, including one in which the forms and energies of the molecular orbitals of the nitrogen molecule were followed all the way to the united atom. Also he has been concerned with the rote of kinetic energy in the Franck–Condon effect, with applications to the fluorescence spectrum of the'dine molecule.