Collision Induced Dissociation of Ions

The study of collision induced dissociation by means of high resolution mass spectrometry has developed in recent years to a method which yields detailed information on the collisional dissociation of molecules. The method is based upon the phenomenon of Aston bands appearing in mass spectra. Introduction of a collision chamber in the drift region between ion source and magnetic analyser localizes the place where collisional dissociation takes place, and offers the possibility to measure the doubly differential cross section for this process with respect to velocity and scattering angle of the charged fragment; integrated however, over all impact parameters. At the energies considered (keV range) these measurements then yield detailed information about the influence of angular position and internuclear distance on collisional excitation of molecules. The experimental results on collision induced dissociation of H + 2 and HeH + are discussed in connection with the existing theoretical approaches. It is shown that there is experimental evidence that the different mechanisms as they are defined by Durup contribute to the collision induced dissociation of these molecules. More experimental work, however, has to be performed in order to disentangle completely the different contributions to collisional dissociation.