Nuclear dynamics of the H^-₂ collision complex beyond the local approximation: Associative detachment and dissociative attachment to rotationally and vibrationally excited molecules

An improved nonlocal resonance model for the description of the nuclear dynamics of the H^-₂ collision complex is developed. The model is based on the ab initio electron-H₂ scattering data of Berman et al at short internuclear distances, the ab initio data of Senekowitsch et al for the bound ²Σ⁺_u state of H^-₂ at intermediate distances, and exhibits the correct polarization interaction at large internuclear distances. Cross sections for associative detachment (AD) and dissociative attachment (DA) to rotationally and vibrationally excited molecules were calculated for a wide range of energies and angular momenta with full inclusion of nonlocal effects. The calculated AD rate constant at 300 K is 3.8 × 10^-9 cm³ s^-1, which is significantly larger than the experimental value reported by Schmeltekopf et al. A series of narrow low-energy orbiting resonances was found in the AD cross section. Our results compare well with previous calculations of DA cross sections within the nonlocal resonance model. The DA cross section for vibrationally and rotationally hot H₂ (T = 1400 K) has been calculated and compared with the experimental data of Allan and Wong. It is demonstrated that the local-complex-potential approximation is an excellent approximation for the associative detachment process, whereas it fails severely for the DA process in H₂.