<p>This thesis describes two projects, spectroscopy of the astrophysically relevant molecule TiH and its isotopologue TiD, and the dissociative recombination (DR) reaction of astrophysically and atmospherically relevant molecules. Emphasis in the thesis is on the first project.</p><p>A series of laser aided spectroscopic studies of TiH/TiD has been carried out. A search for forbidden transitions in the (green) B-X band of TiH was performed. This was followed by a rather bitter fight for the analysis of the perturbed and congested B-X band of TiD, and this was finally rewarding. A substantial extension of a previously reported analysis of this band was performed. The new analysis includes transitions between higher vibrational levels never previously identified. This made it possible to report the first experimentally derived equilibrium constants for the TiH/TiD molecules. There is a need for such results for metal hydrides in the work of calculating the opacity of the atmospheres of cool M and L type stars.</p><p>The DR storage ring experiments have been carried out at the ion storage ring CRYRING in Stockholm. Measurements of the branching fractions and DR rate constants of molecular ions have been done. These results find use in the modeling of the chemistry in interstellar clouds as well as of atmospheres, like the one of Titan, one of the moons of Saturn, which was recently visited by the spacecraft Cassini.</p>

This thesis describes two projects, spectroscopy of the astrophysically relevant molecule TiH and its isotopologue TiD, and the dissociative recombination (DR) reaction of astrophysically and atmospherically relevant molecules. Emphasis in the thesis is on the first project. A series of laser aided spectroscopic studies of TiH/TiD has been carried out. A search for forbidden transitions in the (green) B-X band of TiH was performed. This was followed by a rather bitter fight for the analysis of the perturbed and congested B-X band of TiD, and this was finally rewarding. A substantial extension of a previously reported analysis of this band was performed. The new analysis includes transitions between higher vibrational levels never previously identified. This made it possible to report the first experimentally derived equilibrium constants for the TiH/TiD molecules. There is a need for such results for metal hydrides in the work of calculating the opacity of the atmospheres of cool M and L type stars. The DR storage ring experiments have been carried out at the ion storage ring CRYRING in Stockholm. Measurements of the branching fractions and DR rate constants of molecular ions have been done. These results find use in the modeling of the chemistry in interstellar clouds as well as of atmospheres, like the one of Titan, one of the moons of Saturn, which was recently visited by the spacecraft Cassini.