Semenov, Nikolai Nikolaevich

Born Apr. 3 (15), 1896, in Saratov. Soviet physicist and physical chemist. Academician of the Academy of Sciences of the USSR (1932; corresponding member, 1929). Public figure. Hero of Socialist Labor (1966). Member of the CPSU since 1947.

Semenov graduated from Petrograd University in 1917. From 1920 to 1931 he worked at the Leningrad Physicotechni-cal Institute, and in 1928 he also became a professor at the Leningrad Polytechnic Institute. In 1931 he became director of the Institute of Chemical Physics of the Academy of Sciences of the USSR, serving also as a professor at Moscow State University from 1944. From 1957 to 1963 he was secretary-academician of the Division of Chemical Sciences of the Academy of Sciences of the USSR. In the years 1960–63 he was chairman of the board of the All-Union Society Znanie, and from 1963 to 1971, vice-president of the Academy of Sciences of the USSR. Semenov became a member of the Soviet Pugwash committee in 1964 and from 1961 to 1966 was a candidate for membership to the Central Committee of the CPSU.

Semenov’s early works, which were in the fields of molecular physics and electron phenomena, dealt with the condensation of vapors on solid surfaces, the ionization of salt vapors under the effect of electron impact and other phenomena, the electric breakdown of dielectrics, and the formulation of its heat theory.

Semenov developed a heat theory for explosive gas mixtures. He and his co-workers used the theory as a basis for carrying out research on the propagation of flame, detonation, and deflagration of, for example, explosives and powders.

Semenov discovered branched chain reactions and the phenomenon of chain combustion (explosion). He established that a characteristic feature of chain combustion is the sudden transition at a given temperature from a nearly complete absence of reaction to an explosive occurrence of the reaction at critical values for pressure of the mixture and size of the reaction vessel. Semenov formulated an especially significant general quantitative theory of chain reactions (unbranched, branched, confluently branched) and showed the wide occurrence and practical importance of the reactions. He established the detailed chemical mechanism involved in many complex chain processes and studied the kinetic properties of free atoms and radicals, which help effect the elementary stages of chain reactions.

Semenov and his co-workers discovered a new type of catalysis—ionic heterogeneous catalysis in polymolecular adsorption layers and thin films—and developed concepts regarding the role of free valences in heterogeneous catalysis. Subsequently, he undertook the study of a new, important class of chain reactions involving processes of energetic branching of the chain. He also studied the kinetics and mechanism of homogeneous catalysis by catalysts that are coordination compounds of metals. Semenov trained many specialists in chemical physics, chemical kinetics, and combustion theory.

Semenov is a member of several foreign academies. He was a deputy to the fifth, sixth, and seventh convocations of the Supreme Soviet of the USSR and has been the recipient of the State Prize of the USSR (1941, 1949), a Nobel Prize (1956), seven Orders of Lenin, the Order of the Red Banner of Labor, and several medals.