W. F. Giauque

An Isotope of Oxygen, Mass 18

THE weak doublets of the atmospheric absorption bands of oxygen have been found to originate from a molecule consisting of an oxygen atom of mass 18 combined with one of mass 16. The interpretation recently published by Mulliken (Phys. Rev., 32, 880; 1928) for the strong bands holds in every detail for the weak band. The isotopic rotation–zero point vibration doublets have been calculated by means of the equations of Loomis (Bull. Nat. Res. Council, 2, chap. v.; 1926) and the atmospheric absorption data of Dieke and Babcock (Proc. N.A.S., 13, 670; 1927). The vibrational frequency used for the lower state is that calculated by Birge (Bull. Nat. Res. Council, 2, 232; 1927) from the available data. From the above, the formulæ for the separation of the isotopic doublets in the four P and four R branches is as follows: The constants as given by Dieke and Babcock are