Nikolai Nikolayevich Semenov (born 15.04.1896) — Soviet chemist and physicist, academician (1932; corresponding member 1929), and in 1963-71 vice-president of the USSR Academy of Sciences. Born in Saratov. Graduated from Petrograd University (1917). In 1920-31 he was head of a laboratory and deputy director of the Leningrad Physico-Technical Institute. From 1931 he was director of the Institute of Chemical Physics of the USSR Academy of Sciences. In 1920-32 he also worked at the Leningrad Polytechnic Institute (a professor from 1928), and from 1944 was a professor at Moscow University.
His research concerned chemical physics, of which he is one of the founders. He carried out fundamental work in chemical kinetics and in combustion and explosion. He discovered (1926—32) branched chain chemical reactions and in the following years built a general theory of branched, degenerate-branched and unbranched chain reactions (Nobel Prize in Chemistry, 1956). He revealed the chemical mechanism of a large number of chain and radical reactions, and discovered chain reactions with energy branching (1963). In 1976 he was awarded the Lenin Prize for work on the kinetics of complex chemical reactions.
He laid the foundations of the modern theory of combustion and explosion. As early as 1928 he formulated the critical conditions of thermal explosion and calculated the pre-explosion heating. Under his direction fundamental work was carried out in the application of chemical physics, which made it possible to solve a number of major technical problems. In 1921, jointly with P. L. Kapitza, he proposed a scheme for an experiment on the action of a magnetic field on a beam of paramagnetic particles, later known as the Stern–Gerlach experiment. He is the creator of a large scientific school (Ya. B. Zeldovich, V. N. Kondratyev, Yu. B. Khariton, K. I. Shchelkin, N. M. Emanuel, D. A. Frank-Kamenetskii and others).
USSR State Prizes (1941, 1949). Twice Hero of Socialist Labour (1966, 1976). In 1960-63 chairman of the board of the Znanie society. The M. V. Lomonosov Gold Medal (1970). A member of many foreign academies of sciences and learned societies.