Differences between collisionally activated and electron-transfer dissociations found for CH(2)X(2)(X = Cl, Br, and I) by using alkali-metal targets

High-energy collisionally activated dissociation (HE-CAD) and high-energy electron- transfer dissociation (HE-ETD) on collisions with alkali-metal targets (Cs, K, and Na) were investigated for CH(2)X(2) (+) (X = Cl, Br, and I) ions by tandem mass spectrometry (MS/MS). In the HE-CAD spectra observed, peaks associated with CH(2)X(+) ions formed by a loss of a halogen atom are always predominant regardless of precursor ions and target metals. The observation of the predominant CH(2)X(+) ions is explained by the lowest energy levels of the fragments of CH(2)X(+) + X among the possible fragment energy levels and internal-energy distribution in HE-CAD. In the charge-inversion spectra, relative peak intensities of the negative ions formed by HE-ETD strongly depend on the precursor ions and the target metals. While the CHCl(2) (-) ion was predominant in the spectra of CH(2)Cl(2) (+) regardless of target species, the most intense peaks in those of CH(2)Br(2) (+) and CH(2)I(2) (+) were ascribed to either Br(-) or CH(2)Br(-) and either I(-) or I(2) (-), respectively, depending on the target metals. The dependence of the relative intensities of the fragment ions by HE-ETD on the precursor ions and target species are discussed on the basis of the energy levels of the neutral fragments and the narrow internal-energy distribution resulting from the near-resonant neutralization. It was demonstrated that HE-ETD using the alkali-metal targets provided rich information on the dissociation of the neutral species.