Rotational Analysis of Absorption Bands of Lead Monoxide

THE low-lying states of N 2 and of CO arise from electron configurations 1 which may be written: In the group of molecules from CO to PbTe, the allowed absorption bands of longest wave-length may then be expected to be 1 Σ + , 1 π – X 1 Σ + . This is found to be the case, for example, in SiS, where the systems D 1 Π – X 1 Σ + and E 1 Σ + – X 1 Σ + appear readily in absorption 2,3 . In addition, evidence about some other predicted states, notably e 3 Σ − , I 1 Σ − and (?) 1 Δ, has been obtained from work 4,5 on the perturbations in D 1 Π. In SiO, GeO and SnO there is no further strong absorption 6 until wave-lengths considerably shorter than those corresponding to the E – X systems, indicating that more highly excited orbitals than (2) or (3) are here involved.