Semyonov also spelled Semë nov
born April 15, 1896, Saratov, Russia
died Sept. 25, 1986, Moscow, U.S.S.R.
Russian physical chemist.
His specialty was the mechanisms of chain and branched-chain chemical reaction s, which he showed were the norm in chemical transformations. He shared a 1956 Nobel Prize with Cyril Hinshelwood (1897–1967).