DIRECT-DETECTION AND SPECTROSCOPY OF O-4

We have produced and directly detected a metastable state of tetraoxyg en in a molecular beam, both by means of a de discharge and by photodi ssociation of ozone in the collision region. The O-4 produces a compl ex spectrum from which general conclusions may be made about its energ etics 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 O-2 molecules. A predominance of peak frequency differences in the range 411-419 cm( -1) supports a cyclic D-2d geometry as predicted by ab initio calculat ions, although a definitive judgment on the structure of O-4 awaits f urther study.