The Absorption Coefficient of Nitrogen Dioxide in the Visible Spectrum

Abstract

The absorption coefficient of nitrogen dioxide in the visible spectrum has been measured at pressures up to 70 mm Hg with a 40A spectrophotometer slit. Beer's law is obeyed in this region. The transmission as measured when using a tungsten source, is the same as that oftained with either a high or low pressure mercury arc, except at the 4339–4358A group of mercury lines, where the absorption coefficient was found to be 15 percent greater with the mercury source. The absorption coefficient curve obtained with either a 40A or 15A slit is essentially sinusoidal in appearance, the absorption maxima and minima generally differing by about 10 percent in intensity. The maxima are separated by 700±100 cm—1. They appear to be due, not to the ground state of the molecule, but to groups of excited levels which are uniformly separated.