Predissociation and Perturbation in the Selenium Molecule

Abstract

IT is known that the predissociation produced by the radiationless transition from an excited stable molecular state to an unstable one is responsible for the broadening of the absorption rotational lines and the increase in intensity of the perturbed bands. In the emission spectrum, the bands vanish in the region of perturbation. This usual case is well illustrated in the band system B³∑⁻_u – X³∑⁻_g of S₂. In the progression v″ = 0, the absorption spectrum shows sharp band heads up to v′ = 9, while the v′ = 10, 11 … bands are very diffuse. At v′ = 10 a strong intensity increase occurs. This predissociation corresponds to the case I(c) of Herzberg¹ due to an interaction between two excited states one of which is stable and the other of repulsive type. The crossing of these two potential energy curves occurs above the dissociation limit of the repulsive level. So far it is the only well-established case of this kind.