COLLISIONAL ACTIVATION SPECTRA OF ORGANIC IONS (REPRINTED FROM THE JOURNAL OF THE AMERICAN-CHEMICAL-SOCIETY, VOL 95, PG 7, 1973)

Collision with neutral molecules is shown to provide a convenient meth od of adding internal energy to ions in a field-free drift region of t he mass spectrometer. The effects on this process of ion accelerating potential, target gas pressure and identity, and precursor ion interna l energy and mass have been investigated to optimize experimental cond itions. Such collisions cause ion decompositions whose activation ener gies cover a broad range; for a particular ion such decompositions can be viewed as its ''collisional activation (CA) spectrum.'' CA spectra , which can be obtained for each ion in the normal mass spectrum, and which appear to follow the predictions of the quasi equilibrium theory , show many more of the possible unimolecular ion decomposition reacti ons for an ion than do unimolecular metastables, and thus provide valu able information for ion reaction mechanisms and molecular structure d etermination. Collisional activation can sometimes yield ion energies which are relatively inaccessible by electron impact. The precursor io n internal energy has a negligible effect on the ion's CA spectrum exc ept for product ions formed through the processes of lowest activation energy. Thus, CA spectra should also be valuable for the characteriza tion of ion structures.