THRESHOLD BEHAVIOR IN SINGLE-PHOTON DOUBLE-IONIZATION OF ATOMIC OXYGEN

The threshold behavior of the single-photon double-ionization cross se ction of atomic oxygen has been studied using vacuum uv radiation from a synchrotron storage ring. The double-ionization cross section appea rs to follow a power law E(alpha) (where E is the kinetic energy of th e two electrons) from its threshold to about 2.0 eV above with an expo nent alpha = 1.08+/-0.03, which is consistent with Wannier's theoretic al value of 1.056. The cross section also shows the influence of the d oubly excited 2s2p(3)nln'l' (n,n' > 3) neutral states, among which the first three converge to the 2s2p(3)(S-5(o))4p(P-6(o)) ionic state of oxygen.