On the absorption of light by gaseous, liquid and solid xenon

The result of studies made by McLennan and McLeod and by McLennan, Smith and Wilhelm on the Raman effects obtained with liquid hydrogen have made it abundantly clear that molecules of hydrogen in the liquid phase exist or can exist in electronic, vibrational and rotational states that are exactly the same as states that are available for them to assume in the form of a gas or as isolated units. The same is true in regard to energy states that molecules of oxygen or of nitrogen may take up when existing as isolated entities on the one hand or when existing as a gas or a liquid on the other. In so far as oxygen is concerned, it is known from the work of Babcock that practically all the molecules of oxygen in the earth’s atmosphere are in the electronic state of lowest energy possible for them to assume. Only a very small percentage of them, namely, 0·04 per cent., have even one quantum of vibrational energy. It has been shown by McLennan, Smith and Wilhelm that a similar statement applies in a description of the energy states of the molecules of oxygen as they exist in the liquid or in the solid phase. The band systems and the structures of the band system that characterise the absorption spectra of gaseous, liquid and solid oxygen are identical. These bands all originate in transitions to higher energy states from rotational vibrational energy levels associated with a fundamental 3 Ʃ electronic energy state that can be shown by the theory of Hund and Mullikan to be the most stable one that molecules of oxygen can assume.