Collision Induced Dissociation

Molecular ion beams in vacuum have the unique advantage that no intermolecular interactions are present, enabling us to study properties that are usually not accessible in bulk material. Collision induced dissociation is one of the means to precisely determine bond dissociation energies experimentally. To perform these experiments, a high vacuum (10-5-10-7 mbar) set up is designed and build in our group, consisting of an electrospray ionization source, a quadrupole mass filter to select the desired ion species, an ion guide in combination with a collision cell and a time of flight mass spectrometer for detections. To achieve meaningful bond dissociation energies, great care has to be taken to appoint exact kinetic energies to the precursor ions before collision with the neutral collision gas. When the kinetic energy reaches a certain threshold, the precursor starts to dissociate into fragments which are then detected as well. In simple terms, recording the precursor as well as fragment ion intensities with increasing collision energy leads to a collision cross section which can be evaluated using theoretically (DFT) derived input data to determine bond dissociation energies.