STUDY OF TARGET GAS EXCITATION ACCOMPANYING COLLISIONAL ACTIVATION OF LARGE POLYATOMIC IONS
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Studies on the dynamics of collision-induced dissociation (CID) of the [M + H]+ion of chlorophyll a are reported. The dynamical information derived from this study is based upon measurements of the energy loss accompanying CID, i.e., the change in the translational energy of the [M + H]+ion upon collision with the target gas. When helium is used as the target gas, the energy loss is quite large (ca. 24 eV), but the measured energy loss decreases as the ionization energy of the target gas is decreased. For example, the energy loss decreases from 24 to 9 eV when He, Ne, Ar, and Kr target gases are used. In addition, the energy loss decreases as the energy of the incident ion is decreased. We interpret the trend in the energy loss data as evidence that target gas excitation and collisional activation are competitive processes. The general conclusions from this work are supported by studies of ionmolecule reactions between translationally excited (keV energies) polyatomic ions (e.g., C6H6+) and thermal neutral atoms and molecules. The latter studies were performed by Fourier transform mass spectrometry (FTMS). Based on these studies a general model for keV energy collisional activation is proposed. 1986, American Chemical Society. All rights reserved.
