Rotational Analysis of Bands of the Absorption Spectrum of PbS

The rotational analysis of four systems in the absorption spectrum of lead sulphide has been carried out. Derived constants, in cm -1 , for 208 PbS are as follows: The internuclear distance in the ground state, r e ", is found to be 2.287 Å, somewhat shorter than the value previously accepted. The results are compared with those for PbO and for SnS and it is suggested that case c coupling is important for some of these states.