The Absorption Spectrum of Diatomic Bismuth

The absorption spectrum of diatomic bismuth, previously observed but not analyzed, has been obtained by heating pure bismuth in an atmosphere of nitrogen in a carbon-tube furnace at temperatures from 850 to 1500°C and also by heating in an evacuated quartz tube up to 1200°C. Four systems of bands have been photographed and analyzed: (1) the visible system, 4500A to 7900A, which consists of over 300 bands which have been arranged in square array extending to $v^{\prime }=59\mathrm{}$ and $v^{\prime \prime }=55\mathrm{}$. (2) The ultraviolet system of 40 bands, 2600A to 2900A, which has its lower state in common with (1). (3) The far ultraviolet system, below 2250A, which is very difficult to obtain and measure but almost certainly has the same lower state as (1) and (2). (4) The violet system, appearing only at temperatures greater than 1000°C ((1), (2) and (3) appear below 900°C), which consists of 15 sharp band heads, 9 "continuous bands" and a series of closely spaced diffuse bands. Its lower state is the upper state of (1) and its upper state is presumably crossed by a repulsive state which accounts for the diffuse and continuous bands. There is also an extended continuum in the neighborhood of 3100A. Assuming that the lowest state dissociates into two normal ${}_{}{}^4{}_{}{}^{}S_{\frac{3}{2}}^{}{}_{}{}^{}$ bismuth atoms, a set of potential energy curves for the molecular states has been drawn with satisfactory extrapolation into atomic states in all cases. The estimated heat of dissociation of the lowest state is 1.71 volts.