Direct detection and spectroscopy of O4*

Abstract

We have produced and directly detected a metastable state of tetraoxygen in a molecular beam, both by means of a dc discharge and by photodissociation of ozone in the collision region. The O₄^* produces a complex spectrum from which general conclusions may be made about its energetics and structure. The detection proceeds through a (1+1) resonant photoionization process in the vicinity of 300 nm, implying an energy for this species about 4 eV above that of two isolated O₂ molecules. A predominance of peak frequency differences in the range 411–419 cm^-1 supports a cyclic D_2d geometry as predicted by abinitio calculations, although a definitive judgment on the structure of O₄^* awaits further study.