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Abstract

Numerous observations have reported the sustained presence of complex molecules in the
interstellar medium (ISM) since the first half of the twentieth century. Especially the production
of large molecules in such harsh environments is still an outstanding fundamental
problem in the scientific community. It is known that the complex chemical processes
observed in the gas-phase of ISM are majorly based on ion reactions. Dissociative recombination
(DR) of molecular ions is a dominant process in such environments that neutralizes
the plasma and leads to the fragmentation of molecules. In this context, metal oxides have
been proposed to play a significant role in the complex reaction mechanisms within the
astrochemical networks. In this work we undertake a detailed study on one such distinctive
system, the titanium monoxide cation (TiO⁺) which can be formed by the chemi-ionization
(CI) process between atomic titanium and oxygen. The process has been proposed to be responsible
for the production of free electrons and severe atomic depletion of Ti in gas phase
ISM. The inverse process, DR, is expected to be endothermic, contrary to most other cases.
Precise laboratory studies on the DR of TiO⁺ are needed for a concrete proof of the reaction
energetics, thus elucidating the molecular reaction dynamics. Apart from offering a first
detailed insight into the unexplored regime of endothermic DR reactions, this would lend
momentous possibilities for better practical applications of TiO⁺, an extremely significant
compound as a precursor for TiO and TiO² which are crucial for material sciences applications
and commercial industries alike. Understanding of such an endothermic DR also
opens up avenues for novel scientific proposals in varied fields such as in communication
systems technology to mitigate atmospheric scintillation.
To the best of our knowledge, no direct investigation of the specific DR for such class
of reactions has been carried out until the time of production of this work, experimentally
or theoretically. Such experiments have been conducted at the Max-Planck-Institute for
Nuclear Physics, Heidelberg as a part of this study at the electrostatic Cryogenic Storage
Ring (CSR) in similar conditions as in the cold ISM. Here, we elucidate the experimental
apparatus, implemented techniques, measurement campaign, obtained data and the interim
results of a TiO⁺ DR experiment performed with the electron beam setup at CSR.