Other Free Encyclopedias » Online Encyclopedia » Encyclopedia - Featured Articles » Contributed Topics from F-J

Franck, James

energy atoms transitions quantized

(1882–1964) German–US physicist: gave first experimental demonstration of the quantized nature of molecular electronic transitions.

Franck studied law at Heidelberg but left after a year in order to study physics at Berlin instead. After service in the First World War (he was awarded the Iron Cross), he became professor of experimental physics at Göttingen. In 1933, being a Jew, he felt obliged to leave Germany, settling eventually in the USA, where he became professor of physical chemistry at the University of Chicago. During the Second World War he worked on the American atomic bomb project, proposing in the Franck Report that the bomb be demonstrated to the Japanese on uninhabited territory before being used on a city.

Franck’s major work concerned the quantized nature of energy absorption by molecules. In 1914, together with Gustav Hertz (1887–1975), he demonstrated that gaseous mercury atoms, when bombarded with electrons, absorb energy in discrete units (or quanta). For mercury atoms this unit of energy is 4.9 eV. Following the absorption, which leaves the mercury atom in an energetically excited state, the atom returns to its original (or ground) state by emitting a photon of light. This experiment constituted the first experimental proof of ideas on energy levels in atoms, and Franck and Hertz were awarded the 1925 Nobel Prize for physics for their work.

Later, in conjunction with E Condon (1902–74), Franck also studied the energy requirements for vibration and rotation of diatomic molecules, showing that these were also quantized and that dissociation energies (the energy required to break the chemical bond between the two atoms), could be extrapolated from them. The Franck–Condon principle states that the most probable electronic transitions are those in which the vibrational quantum number is preserved, since electronic transitions take place on a much shorter time-scale than vibrational ones.

Frank, Free(1777–1854) - Entrepreneur, pioneer, Chronology, Pioneering Illinois, Founding New Philadelphia [next] [back] Francis, Philip L. - President and Chief Executive Officer of PetSmart, Career, Sidelights

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or