Band Spectrum ofPb2in Absorption and Emission

A band system has been observed when light is absorbed by lead vapor heated to about 1400°C. The same band system has also been found in emission. Some ninety band heads have been located between the wavelengths of 4600 and 5200A. The bands are degraded toward the red. The vibrational analysis has been made but the complexity of the isotope effect has prevented a rotational analysis. Within the error of observation the heads are represented by the formula: $\nu =19,570.8+159.22(v^{\prime }+\frac{1}{2})-0.882\mathrm{}{(v^{\prime }+\frac{1}{2})}^2+0.00518\mathrm{}{(v^{\prime }+\frac{1}{2})}^3-256.5(v^{\prime \prime }+\frac{1}{2})+2.96\mathrm{}{(v^{\prime \prime }+\frac{1}{2})}^2.$ Fairly conclusive evidence is presented for the ascription of this band system to the molecule ${\mathrm{Pb}}_2$.