James Franck (26.07.1882-21.05.1964) was a German physicist. He was born in Hamburg. In 1901 — 02 he studied at the University of Heidelberg, graduated from the University of Berlin (1906) and worked there until 1917 (from 1916 as professor); in 1917 — 21 he headed the physics department at the Institute of Physical Chemistry (Berlin). In 1921 —34 he was professor at the University of Göttingen and director of the Physical Institute. In 1935 he emigrated to the USA, where in 1935 —38 he was professor at Johns Hopkins University and in 1938 — 47 at the University of Chicago.
His work concerned atomic and nuclear physics, molecular spectroscopy and its application to chemistry, and photosynthesis. Together with Gustav Hertz he carried out (1912—14) a series of experiments on the excitation and ionisation of mercury vapour atoms by electron impact (the Franck — Hertz experiments) and discovered the laws of collisions of electrons with atoms, which served as proof of the discreteness of the energy levels of atoms and confirmed Bohr's theory of the atom (Nobel Prize, 1925). He studied atomic jumps and energy levels in atoms and the transfer of energy in atomic systems in fluorescence, developed a spectral method of investigating chemical forces, and investigated photochemical processes in the chlorophyll molecule. In 1925 he proposed a mechanism explaining the photochemical dissociation of iodine molecules, later developed by E. Condon (the Franck — Condon principle). In 1945 he spoke out against the use of the atomic bomb.
He was a member of a number of academies of sciences and scientific societies, in particular a foreign corresponding member of the USSR Academy of Sciences (1927). The M. Planck and B. Rumford Medals (1955).