How was Gerhard Herzberg awarded the Noble Prize?

Name: Gerhard Herzberg. 
Country: Canadian.
Date of Birth: 25 December 1904.
Date of Death: 3 March 1999.
The subject of Study: Diatomic molecule, electronic configuration, radical, spectroscopy.
Noble Prize Year: Nobel Prize for Chemistry in 1971 for their work in determining the electronic structure and geometry of molecules, especially free radicals groups of atoms that contain odd numbers of electrons.