"Letters to the Editor" issued as Part 2 and separately paged from v. 148, 1967.

Multiplets of Transition-Metal Ions in Crystals provides information pertinent to ligand field theory. This book discusses the fundamentals of quantum mechanics and the theory of atomic spectra. Comprised of 10 chapters, this book starts with an overview of the qualitative nature of the splitting of the energy level as well as the angular behavior of the wavefunctions. This text then examines the problem of obtaining the energy eigenvalues and eigenstates of the two-electron systems, in which two electrons are accommodated in the t2g and eg shells in a variety of ways. Other chapters discuss the ligand-field potential, which is invariant to any symmetry operation in the group to which symmetry of the system belongs. This book discusses as well the approximate method of expressing molecular orbitals (MO) by a suitable linear combination of atomic orbitals (AO). The final chapter discusses the MO in molecules and the self-consistent field theory of Hartree–Fock. This book is a valuable resource for research physicists, chemists, electronic engineers, and graduate students.

are intended to fill the gap between a manufacturer's handbook, and review articles that highlight the latest scientific developments. A fourth volume will deal with techniques for specimen handling, beam artifacts, and depth profiling. It will provide a compilation of methods that have proven useful for specimen handling and treatment, and it will also address the common artifacts and problems associated with the bombardment of solid sur faces by photons, electrons, and ions. A description will be given of methods for depth profiling. Surface characterization measurements are being used increasingly in di verse areas of science and technology. We hope that this series will be useful in ensuring that these measurements can be made as efficiently and reliably as possible. Comments on the series are welcomed, as are suggestions for volumes on additional topics. C. J. Powell Gaithersburg, Maryland A. W. Czandema Golden, Colorado D. M. Hercules Pittsburgh, Pennsylvania T. E. Madey New Brunswick, New Jersey J. T. Yates, Jr.

This thesis presents optical methods to split the energy levels of electronic valleys in transition-metal dichalcogenides (TMDs) by means of coherent light-matter interactions. The electronic valleys found in monolayer TMDs such as MoS2, WS2, and WSe2 are among the many novel properties exhibited by semiconductors when thinned down to a few atomic layers, and have have been proposed as a new way to carry information in next generation devices (so-called valleytronics). These valleys are, however, normally locked in the same energy level, which limits their potential use for applications. The author describes experiments performed with a pump-probe technique using transient absorption spectroscopy on MoS2 and WS2. It is demonstrated that hybridizing the electronic valleys with light allows one to optically tune their energy levels in a controllable valley-selective manner. In particular, by using off-resonance circularly polarized light at small detuning, one can tune the energy level of one valley through the optical Stark effect. Also presented within are observations, at larger detuning, of a separate contribution from the so-called Bloch--Siegert effect, a delicate phenomenon that has eluded direct observation in solids. The two effects obey opposite selection rules, enabling one to separate the two effects at two different valleys.

Issues for Sept. 1951- include the Bulletin.