Fw. Mclafferty et al., COLLISIONAL ACTIVATION SPECTRA OF ORGANIC IONS (REPRINTED FROM THE JOURNAL OF THE AMERICAN-CHEMICAL-SOCIETY, VOL 95, PG 7, 1973), Journal of mass spectrometry., 30(6), 1995, pp. 797-806
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.