Rotational Analysis of Absorption Bands of Lead Monoxide

Abstract

THE low-lying states of N₂ and of CO arise from electron configurations¹ 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 ¹Σ⁺, ¹π – X ¹Σ⁺. This is found to be the case, for example, in SiS, where the systems D ¹Π – X ¹Σ⁺ and E ¹Σ⁺ – X ¹Σ⁺ appear readily in absorption^2,3. In addition, evidence about some other predicted states, notably e ³Σ⁻, I ¹Σ⁻ and (?)¹Δ, has been obtained from work^4,5 on the perturbations in D ¹Π. In SiO, GeO and SnO there is no further strong absorption⁶ 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.