The Nobel Prize in Chemistry 1971 was awarded to Gerhard Herzberg "for his contributions to the knowledge of electronic structure and geometry of molecules, particularly free radicals".
 

Herzberg began as a physicist and his first contributions to molecular spectroscopy were published at the end of the 1920's. For a chemical reaction to occur the original molecules must in some way break up into fragments which rearrange to form the new molecules. These fragments, or intermediates, are called free radicals. Herzberg has so far performed extensive precision determinations of the properties of over thirty free radicals among which are to be found the radicals methyl and methylene - well known from organic chemistry.