Dissociation mechanisms of excited CH3X (X = Cl, Br, and I) formed via high-energy electron transfer using alkali metal targets

Abstract

High-energy electron transfer dissociation (HE-ETD) on collisions with alkali metal targets (Cs, K, and Na) was investigated for CH(3)X(+) (X = Cl, Br, and I) ions by a charge inversion mass spectrometry. Relative peak intensities of the negative ions formed via HE-ETD strongly depend on the precursor ions and the target alkali metals. The dependency is explained by the exothermicities of the respective dissociation processes. Peak shapes of the negative ions, especially of the X(-) ions, which comprise a triangle and a trapezoid, also strongly depend on the precursor ions and the target alkali metals. The trapezoidal part of the I(-) peak observed with the Na target is more dominant and much broader than that with the Cs target. This dependence on the targets shows an inverse relation between the peak width and the available energy, which corresponds to the exothermicity assuming formation of fragment pair in their ground internal states. From a comparison of the kinetic energy release value calculated from the trapezoidal shape of I(-) with the available energy of the near-resonant level on the CH(3)I potential energy curve reported by ab initio calculations, the trapezoidal part is attributed to the dissociation to CH(3) + I((2)P(3/2)) via the repulsive (3)Q(1) state of CH(3)I, which is not dominant in the photo-dissociation of CH(3)I. The observation of trapezoid shape of the CH(2)I(-) peak with the Cs target indicates spontaneous dissociation via repulsive potential from the (3)R(2) Rydberg state, although the correlation between the (3)R(2) Rydberg state and relevant repulsive states has not been reported by any theoretical calculation.

High-energy electron transfer dissociation of protonated amino acids

“…These trapezoidal profiles indicated that the dissociation of the 17 u loss from the precursor ions suggested a spontaneous process from a state with a specific internal energy, as found in the previous results for methanol [39], CH 2 X 2 [43], and CH 3 X ions [45]. To discuss the dissociation mechanism in conjunction with AEs, KER values are …”

“…The ratio of the KER values to the averaged AE value is 62%. This large ratio implied that most of the internal energy was released as kinetic energy at the dissociation via repulsive potential, similar to that of the small organic cations [36,39,43,45]. On the other hand, C N bond cleavage from the hypervalent ammonium radical in methyl ammonium to result in the NH 3 loss was reported from the neutral detection experiment by Porter and coworkers [16] and from the NRMS method by Turecek [35].…”

“…The respective KER values for the NH 3 and H 2 losses also agreed with each other, as shown in Table 2. Charge inversion spectra of the small organic molecular ions, such as CH 2 X 2 [43,44] and CH 3 X [45], where X is a halogen atom, showed a clear difference depending on the precursor ions and the target atoms. In these studies, the target dependence for the peak shapes and the relative peak intensities were clearly observed in their charge inversion spectra.…”

“…Using this technique, unstable neutral intermediates, such as vinylidenes [40,41], CH n (n = 3-5) [42], CH 2 X 2 (X = Cl, Br, and I) [43,44], and CH 3 X (X = Cl, Br, and I) [45], have been studied. Protonated molecules [AB+H] + , which are positive ions formed from stable molecules (AB), are in a singlet state (as are stable molecules) because the proton does not have an electron associated with it.…”

Study of Ion Dynamics by Electron Transfer Dissociation: Alkali Metals as Targets

“…Charge inversion mass spectrometry has also provided information concerning the dissociation pathways of energy-selected neutral species, such as CH n (n=3-5), 44) C 2 H 2 , 45) C 3 H 4 , 46) chlorophenol, 47) and methyl stearate. 48) e dissociation of energy selected neutral of halogen containing simple molecules, such as CH 2 X 2 49,50) and CH 3 X (X=Cl, Br, I) 51) showed a strong dependence on both the target species and halogen in the molecules in charge inversion spectra using alkali metal targets (Cs, K and Na). While the CHCl 2 − ion was predominant in the spectra of CH 2 Cl 2 + regardless of target species, the most intense peaks were CH 2 Br 2 + and CH 2 I 2 + were ascribed to being derived from either Br − or CH 2 Br − and either I − or I 2 − , respectively, depending on the target metal used.…”