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 2s²A₁', 2p²A₂'' and 3p²E' bound Rydberg states of H₃ and the two 2s²A₁' and 2p²A₂'' states for D₃. This data provide an empirical benchmark for the refinement of theoretical models involving non-adiabatic interactions and dynamics for H₃.