While at Munich, Kratzer extended the theory of diatomic molecular spectroscopy by including anharmonic forces between the nuclei, which changed the oscillation frequencies.
[3][4][5] Based on his work at Munich, it was in 1922 that Kratzer's detailed analysis on the cyanide spectroscopic bands was published.
His analysis resulted in the introduction of half-integral quantum numbers to account for molecular rotation.
[7] Here, Kratzer made contributions to quantum mechanics and became a leading authority in the field of molecular band spectroscopy.
[4] At this time, there were three centers of development for quantum mechanics and the interpretation of atomic and molecular structure, based on atomic and molecular spectroscopy, especially the Sommerfeld-Bohr model: the Theoretical Physics Institute at the University of Munich, under Arnold Sommerfeld, the Institute of Theoretical Physics at the University of Göttingen, under Max Born, and the Institute of Theoretical Physics, under Niels Bohr.