Isotope Effects in the Band Spectra of Boron Monoxide and Silicon Nitride

Abstract

IN 1914 Jevons¹ made measurements on a band spectrum which he attributed to boron nitride. He correlated most of the bands into two systems (“” and “”); a number of weaker bands remained. Recent investigation by the writer² shows that the spectrum—which is probably due to the compound BO—really consists of two superposed spectra.³ These are related to each other exactly as would be predicted by the quantum theory of band spectra if the more intense spectrum is due to the more abundant isotope B¹¹O, and the less intense to the less abundant isotope B¹⁰O. Every one of the approximately 80 bands of B¹¹O, including those both of the and of the systems, is matched, so far as can be determined⁴, by a corresponding B¹⁰O band of about the expected intensity.⁵ In each system, the central band, corresponding to an electronic change alone in a vibrationless molecule, is practically coincident for the two isotopes.⁶ From this centre the bands extend both toward lower and toward higher frequencies, the pattern being exactly the same for both isotopes, the scale or spacing of this pattern, however, being larger for the lighter isotope in a ratio approximately equal to the ratio of the molecular vibration frequencies. This is exactly as predicted by the quantum theory. The maximum separation between corresponding bands of the two isotopes is more than 300 wavenumber units in each system (this amounts to about 200 Å. U. near 8500 in the system).