The molecular spectrum of iodine excited by fluorescence (in the presence of nitrogen) and by active nitrogen

Abstract

The fluorescence spectrum of iodine vapour in the presence of a large excess of foreign gas has been described by Oldenberg (1924) and by Duschinsky and Pringsheim (1935). Oldenberg noted a strong “continuum” with maximum intensity at about 3425 A, on which was superposed a series of diffuse bands, some weak bands about 9 A apart in the neighbourhood of 2700 A, several diffuse bands between 4900 and 4300 A, and a continuum at about 5100 A. The last, unlike the other bands, was shown to be present only when nitrogen was employed as foreign gas, and was attributed to a photochemical reaction between iodine and nitrogen. The “ continuum” 3425 A (sometimes referred to as 3412 or 3460 A—the latter figure refers to the long wave-length limit of the spectrum) has often been observed in iodine spectra, e.g. in emission in a high-frequency discharge (Curtis and Evans 1933), in a Geissler tube (Konen 1898) and in absorption in iodine vapour at high temperature (Skorko 1933; Warren 1935), when it shows clear signs of structure. The diffuse band at 4300 is also well known in the literature of iodine spectra as the continuum 4300 A, and accompanies 3425 in emission spectra. It does not appear to have been observed in absorption.