Towards state selective measurements of the H₃⁺ dissociative recombination rate coefficient

Ion storage and trapping techniques in connection with efficient internal state control and diagnostic for molecular ions offer the potential of providing rate coefficients for the dissociative recombination of H₃⁺ for well-defined initial rotational states, required for understanding the role of this ion in the interstellar medium and other cold environments. Information on the vibrational and rotational excitation in stored H3+ ion beams, as obtained from experiments at the ion storage ring TSR, is reviewed. In addition, the arrangement of the TSR injector trap, using buffer gas cooling in a cryogenic radiofrequency multipole structure to inject pulses of internally cold H3+ ions into the TSR via a high-energy accelerator, is outlined. An account is given of tests towards the in-situ diagnostic of rotational level populations, where laser transitions between low-lying rovibrational levels could be detected in dilute H₃⁺ ion ensembles using chemical probing in the radiofrequency multipole ion trap