Using buffer gas cooled molecular ions in high order multipole ion traps allows to thermalise translational and rovibrational degrees of freedom. In this thesis quantum state selective photodetachment spectroscopy is applied to anionic systems to gain insight into matter-light interactions as well as reaction and collision dynamics at cryogenic temperatures.The absolute photodetachment cross sections of CN and C3N are studied by performing photodetachment tomography. These investigated anions have recently been discovered in the interstellar medium, where photodetachment is a key destruction mechanism.
Absolute collision rate coefficients of rotationally inelastic collisions of OH and OD with helium are measured at low temperatures. The collisionally induced thermodynamic quilibrium of the populated rotational states is perturbed and probed by rotational state selective photodetachment.
Moreover, we have determined the three-body reaction rate coefficient of OD with D2 at cryogenic temperatures. Internal proton transfer of the (OD)D2 complex is proven by isomer specific photodetachment spectroscopy.
Pure rotational spectra of OD are evaluated by a two-photon action spectroscopy scheme using a cw-THz laser system.
Furthermore, ion temperature simulations in a multipole ion trap are carried out and ideas on collisionally induced finestructure thermalisation and btranslational thermometry of O as well as reaction experiments involving electrons are presented.