John H. Van VleckBorn 13 Mar 1899; died 27 Oct 1980 at age 81.John Hasbrouck Van Vleck was an American physicist and mathematician who pioneered in the modern quantum mechanical theory of magnetism, and shared the 1977 Nobel Prize for Physics (with Philip W. Anderson and Sir Nevill F. Mott) for his work on the behaviour of electrons in magnetic, noncrystalline solid materials. In about 1930, he introduced the contribution of the second-order Zeeman effect into the theory of the paramagnetic susceptibility for the ions of the elements samarium and europium, thus bringing calculations into agreement with experimental results. Hans Bethe's theoretical work (c.1929), was extended by Van Vleck to develop the ligand, or crystal, field theory of molecular bonding. He also studied the theory for the nature of the chemical bond, especially as related to its magnetic properties, and contributed to theory of the spectra of free molecules.« |
