Differential cross section for dissociative attachment in HI: H⁻(I²P3/2, I²P1/2) formation

An electrostatic impact spectrometer is used to study the formation of H - ions by dissociative attachment in HI between 3 and 9 eV. Three repulsive electronic resonance states of HI - are found to dissociate adiabatically to H - ( 1 S)+I( 2 P 3/2 ) for the lowest 1 Omega 1/2 and the following Omega 3/2 states, and to H - ( 1 S)+I( 2 P 1/2 ) for the highest 2 Omega 1/2 state. The dominant Sigma symmetry of the experimental angular distributions of H - ions dissociating through the two Omega = 1 / 2 states is significant of strong spin-orbit coupling between these two resonance states of HI - . The lack of Pi -type contributions in these angular distributions, as well as the negligible value of the cross section for H - formation via the Omega = 3 / 2 resonance state, may mean that an electron cannot be bound in the expected Pi symmetry resonance states of HI - . Above an energy of 6.5 eV, both the Omega 3/2 and the 2 Omega 1/2 states interact with bound Feshbach resonances associated with Rydberg states of HI; the interaction can be described as a predissociation by electronic coupling.