Experimentally probing the three-body predissociation dynamics of the low-lying Rydberg states of H3 and D3

Charge-exchange neutralization of H₃⁺ with Cs allows preparation of the low-lying Rydberg states of H₃. These states are predissociated by the repulsive ground state and may play roles as intermediates in the dissociative recombination of H₃⁺ + e^-. Translational spectroscopy and measurements of product momentum partitioning in three-body dissociative charge exchange of fast (12 keV) H₃⁺ and D₃⁺ with Cs yields insights into the nuclear motion during dissociation for the three lowest-lying 2s ²A₁', 2p ²A₂'' and 3p ²E' bound Rydberg states of H₃ and the two 2s ²A₁' and 2p ²A₂'' states for D₃. This data provide an empirical benchmark for the refinement of theoretical models involving non-adiabatic interactions and dynamics for H₃.