The spectrum of the luminescence produced when silicon tetrachloride vapour reacts with glowing active nitrogen was first studied by Jevons. He measured the heads of a group of bands occurring in the more refrangible part of the visible spectrum. These bands have single heads and are degraded towards the long wave-lengths. From the fact that a nitrogen-containing substance is deposited on the walls of the after-glow tube during the reaction, Jevons favoured the view that the bands are due to a nitride of silicon (SiN). This has been verified in a recent study of its spectrum by Mulliken. In this work, which was primarily concerned with the isotope effect, Jevons’ measurements were revised and extended to include two faint companion systems of bands, due to isotopic molecules containing silicon of atomic weights 29 and 30. Further, Mulliken was able to establish spectroscopically the existence of the latter isotope, when the mass-spectrograph evidence was still inconclusive, and he included a description of a weaker system of bands distinct from the above, in that the heads are double and no frequency intervals occurred which agreed with those of the stronger system. Vibrational quantum numbers were assigned for the two systems, and the constants of the rotational structure of the stronger bands were determined by a procedure which was necessarily approximate, since spectrographs of moderate resolving power were used.
Structure of the violet bands of silicon nitride