Ultraviolet photodissociation of H₃⁺

As a step towards in situ probing of the rotational-state distribution of H₃⁺ ions in a stored beam, we have realized their photodissociation in a storage ring by a parallel ultraviolet laser beam. The decay of the photodissociation signal of H₃⁺ for 4.9 eV photons into the channel H⁺₂ + H was identified and showed a time constant of about 2 ms, typical for vibrational levels of H₃⁺ over a wide range of binding energies. The photodissociation products of H₃⁺ at this photon energy were further investigated for a single pass ion beam by kinetic energy release and charge-exchange measurements.