ABSTRACT
Prequantum theory associated infrared absorption with molecular vibration, with motion of the molecule as a whole,distinct from the electronic vibrations responsible for optical spectra. The principle of noninteracting forms of motion extended also to Bjerrum’s vision of a rotating oscillator, vibration being the primary cause of infrared absorption. 1 Heurlin-ger’s treatment of visible bands was built around the Bjerrum model. Thus early quantum theory approached infrared and electronic spectroscopy from similar viewpoints, even though experimental development of the infrared was comparatively superficial, whereas observations of electronic spectra were embarrassingly rich in detail.
