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Abstract

The work presented in this dissertation describes the ongoing efforts aimed towards understanding the Dissociative Recombination by electrons of the deuterated isotopologues of the triatomic hydrogen cation – H₂D⁺ and D₂H⁺ – inside the Cryogenic Storage Ring (CSR), located at the Max Planck Institute for Nuclear Physics. The facility is equipped with a merged electron–ion beams setup, that permits the investigation of ion–electron collisions. The molecular ions were stored for up to 1000 s in the CSR environment at temperatures T<10 K. At such timescales, the rovibrational populations of the stored ion beams become confined to a small number of identifiable states, according to a radiative cooling model based on comprehensive line –lists. The thesis describes the construction of such radiative cooling models, which in addition to radiative relaxation include the effects of inelastic electron collisions and selective depletion by electron recombination. The experimental part of the present work consists of investigating the Dissociative Recombination reaction of rotationally cold H₂D⁺ and D₂H⁺ ions in the relative collision energy range of 0–14 eV. Comparisons between experimental results and state-of-the-art theoretical calculations of the rotational state–specific cross sections are presented. The experimental rate coefficients are converted to plasma rate coefficients and compared against prior estimates that have been used in modelling of interstellar cloud chemistry.