Coupling of Electronic and Nuclear Motions in Diatomic Molecules

Abstract

While for many important problems the quantum mechanical coupling between the motion of the nuclei and of the electrons in a diatomic molecule may be ignored, there are others in which this coupling is the main factor. Among the various phenomena which are conditioned by this coupling and which have recently attracted attention the following may be mentioned:

• 1. The mechanism of the dissociation of molecules by light absorption. This question has been discussed by Franck who, with his co-workers, is also doing important experimental work in this field.¹

• 2. The mechanism of dissociation of molecules as a primary consequence of excitation by electron collision. The ideas of Franck on (1) have here been applied by Birge and Sponer² to a discussion of the experimental results of Hogness and Lunn.

• 3. The relative transition probabilities for the various vibrational transitions associated with a single electron transition in the emission or absorption of light by a molecule; i.e., the problem of intensity distribution in electronic band systems. This question has been treated recently by the writer.³

• 4. The mechanism of the process whereby molecules may be excited to vibration levels by electron couision without simultaneous electronic excitation. That this process actually occurs is proved by the recent experiments of Harries, carried out in Franck’s laboratory.⁴