Walter Heitler

Walter Heinrich Heitler (2 January 1904 – 15 November 1981) was a German – Irish physicist.

His research demonstrated the power of quantum mechanics by developing and applying it with great success in a number of diverse areas, including the valence bond theory, radiation theory, cosmic rays and quantum field theory.

Biographical dates:

Born 02.01.1904 in Karlsruhe; PhD Munich 1926; Habilitation Göttingen 1929; Research Fellow Bristol 1933 – 1941; Professor Dublin Institute for Advanced Studies 1941 – 1949; Director Dublin Institute for Advanced Studies (successor of E. Schrödinger) 1946 – 1949; Professor of Theoretical Physics and Director of the Institute for Theoretical Physics University of Zürich 1949 – 1974; died 15.11.1981 in Zollikon near Zürich.

Honorary doctorates: The universities of Dublin (1954), Göttingen (1968), Uppsala (1973).

Fellow: Royal Irish Academy (1943), Royal Society of London (1948).

Honorary member: Kungl. Vetenskaps Societetens of Uppsala (1967), Leopoldina in Halle (1968), Akademie der Wissenschaften und der Literatur of Mainz (1970), Det Kongelige Norske Videnskabers Selskab (1974), etc.

Prizes: Max Planck Medal (1968), Marcel Benoist Preis (1970), Gold Medal of the Humboldt Gesellschaft (1979), etc.

Main scientific achievements

Quantum chemistry: The first quantum mechanical explanation of the covalent chemical bond goes back to the work of Heitler. In collaboration with F. London he calculated (1927) the interaction of two hydrogen atoms; the result was the qualitatively correct value for the binding energy of the hydrogen molecule. In the same paper also the saturation properties of the chemical bond were understood correctly; the examples treated were the He-H system and the He-He system. Heitler’s further contributions to quantum chemistry and a comprehensive appreciation of his merits in this field can be found in Max Born’s review article ‘Chemische Bindung und Quantenmechanik ‘ (Ergebn. Ex. Naturw. 10, 387 (1930)). From this one can conclude that Heitler was the driving force also for his publications written in collaboration with other authors (e.g. G. Rumer). Later prominent scientists (e.g. L. Pauling) could build on the methods of the Heitler-London paper.

Quantum electrodynamics: Heitler’s first work in quantum electrodynamics was the calculation (together with H. Bethe) of the pair production of γ-rays in the Coulomb field of an atomic nucleus (Bethe – Heitler formula). In 1936 Heitler’s classic book ‘Quantum Theory of Radiation’ was published (new editions in 1944 and1954 and five later reprints, the latest being a Dover reprint in 1984). For the first time the quantum theory of the interaction between radiation and matter was treated from a unified point of view and applied to numerous physical processes. At the same time Heitler (in collaboration with H. J. Bhabha) developed the cascade theory of electron showers. This work proved that many phenomena seen in cosmic ray experiments could be explained without the necessity of introducing new interactions. This was particularly emphasised by Pascual Jordan in the ‘Laudatio for Walter Heitler’ on the occasion of the award of the Max Planck Medal (see Pascual Jordan ‘Begegnungen’, Stalling Verlag 1971). The exact theory of line breadth, worked out by Heitler and his collaborators during the years 1949 – 1953 is a further example of his lasting influence on quantum electrodynamics.

Meson theory: Already the first paper of Heitler ((1938) in collaboration with H. Fröhlich and N. Kemmer) contains the theoretical prediction of the electrically neutral π-meson. Shortly afterwards he developed (in collaboration with H. W. Peng) the radiation damping theory which lead to the famous 'Heitler integral equation' for scattering processes. A further milestone in the understanding of the π-meson – nucleon interaction is a paper (1946) in which Heitler deduces relations between the scattering cross sections as a consequence of the isospin invariance of the interaction. Here he shows once more his supreme mastery of group theoretical methods, which had helped him already in his work on quantum chemistry.

See also

L. O’Raifeartaigh and G. Rasche: Walter Heitler 1904-81, in “Creators of Mathematics, The Irish Connection”, ed. Ken Houston, University College Dublin Press, 2000.

Sir Nevill Mott, F.R.S.: Walter Heinrich Heitler 1904-1981, in “ Biographical Memoirs of Fellows of the Royal Society”, Volume 28, 141 (Nov. 1982).

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