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

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Abstract
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-(1S)+I(2P3/2) for the lowest 1 Omega 1/2 and the following Omega 3/2 states, and to H-(1S)+I(2P1/2) 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.