The decay pathways of the structured ionization region of oxygen at different momentum transfers,i.e.,0,0.23 a.u.（atomic unit）,and 0.91 a.u.,are studied by measuring the ion and the scattered electron coincidently.It is found that the dipole-forbidden superexcited states of（2σu）^-1（c^4Σu^-）npσu ^3Σg^-← X^3Σg^-decay into different channels according to the principal quantum number n.The broad ridge above 35 eV,which may be due to inner-valence excited states of（2σg）^-1nλ or multiply excited states,is observed both at small and large momentum transfers,and its decay channel of O＋＋ O is dominant.
