The investigation of the elementary reactions of reactive intermediate species began about half a centruy ago with the advent of free radical kinetics as an active area of chemical research. In spite of the relatively greater ease of detection of a species carrying an electrical charge, and the fact that organic chemists had for decades postulated mechanisms involving ionic intermediates, the systematic study of the elementary reactions of ions was delayed for more than twenty years after the first beginnings of free radical kinetics. Even at this writing, in 1978, the word "kinetics" is considered by many chemists to be synomomous with "kinetics of neutral species". Yet in spite of the relatively late start and separation from the mainstream of kinetics, the field of ion physics and chemistry is fluorishing, and growing at an ever faster pace. Instrumentalists devise ever more sophisticated apparatuses with capabilities of delving into nearly every aspect of the interactions between ions and molecules. Even satellites orbiting the earth are now being used effectively to determine rate coefficients of ionospheric ion-neutral reactions, some of which can not as yet be measured in the laboratory.

Chemical reactions between ions and neutral gas are very important in the interstellar medium, since they usually have much lower barriers than neutral-neutral reactions. Thus, they are more likely to take place at low temperatures. In this work, the endothermic reactions of CH2D+, H2D+, and N+ with H2 have been investigated in a temperature variable 22-pole ion trap. Under the chosen conditions inside the trap the chemical processes are comparable to those in typical astrophysical environments. At low temperatures, the reactions mentioned above depend very sensitively on the translational and internal energies of the reaction partners. This dependence can be utilized to gain information on the energy levels or the population of the internal states. Based on this sensitivity, two different types of investigations were performed in this work. High resolution spectra of CH2D+ were obtained, resulting in improved predictions for pure rotational transitions. First steps were made towards a detailed understanding of the processes in laser induced reactions, often leading to non-Gaussian line profiles. In addition, the influence of internal states on ion-molecule reactions allowed to determine the purity of para hydrogen samples and yielded insight into the reaction kinetics of the system N+ + H2.