Alternating Intensities in Band Lines

Abstract

BANDS in the spectra of neutral and ionised nitrogen show unexplained alternating intensities, and the bands of helium are best interpreted if one assumes that only half the lines are observed, the alternate lines being not merely weak but missing altogether (Mecke, Zeits. f. Phys. 26, 227, 1925; 31, 709, 1925). A similar effect seems to be present in oxygen, although the interpretation is less certain. All these molecules are symmetrical, composed of two like atoms. I wish to suggest that the alternations may be connected with the well-known difficulty of assigning the proper period in quantising the rotation of a symmetrical system (Ehrenfest and Tolman, Phys. Rev. 24, 287, 1924).