IDENTIFICATION OF THE 4P-SIGMA(U) (1)PI(U) RYDBERG STATE OF O-2

New high-resolution measurements of the O-2 photoabsorption cross sect ion in the 1147-1155 Angstrom region are presented. The observation of three previously-unreported narrow lines in a band near 1148 Angstrom has enabled unambiguous assignment of the band to a (1) Pi(u)<--X(3) Sigma(g)(-) transition which gains strength through a spin-orbit inter action with the upper state of a (3) Pi(u)<--X(g)(3-) transition appea ring at 1153 Angstrom. Other lines in the 1148 Angstrom band are broad ened by predissociation through a heterogeneous interaction with a nea rly energetically coincident (1) Delta(u) level. The states, labelled h (1) Pi(u), F-3 Pi(u), and i(1) Delta(u), are predominantly of 4p lam bda Rydberg molecular orbital configurations although there are indica tions that the Pi(u) states interact strongly with valence states of t he same symmetry. (C) 1995 American Institute of Physics.