Abstract
This thesis presents work on merged-beams experiments using the DESIREE facility, which consists of two electrostatic
ion-storage rings operated at cryogenic temperatures of about 13 K. The two storage rings have a common straight
section, where oppositely charged ions can interact at sub-eV collision energies. The work consists of development of
the experimental method, tools for data analysis, and simulations for interpretation of the experimental results. This
development has led to the first results from merged-beams experiments at DESIREE. The experiments are performed on
mutual neutralization, a collision process where an electron is transferred from a negatively charged ion to a positively
charged ion, resulting in two neutral products. This reaction is investigated for three systems: Li+ with D−, Na+ with D−,
and Mg+ with D−. The reactions studied are of astrophysical interest, in particular for modeling of stellar atmospheres. The
detection of the reaction products is done by using a position- and time-sensitive detector, and from this information it
is possible to determine the quantum states involved in the reaction. The branching fractions of the reaction channels are
measured and compared to theoretical modeling.