Charge Inversion Mass Research Articles

Dissociation mechanism of electronically excited CH 2X 2 (X = Cl, Br) formed by near-resonant neutralization using charge-inversion mass spectrometry

The dissociation mechanism of excited CH 2X 2 (X = Cl, Br) was investigated using charge-inversion mass spectrometry, in which positive ions collide with an alkali metal target to generate neutral fragments, and the negative ions formed from the neutral fragments are mass analyzed. Different relative abundances of the negative ions were observed in the charge-inversion spectra for CH 2Cl 2 and CH 2Br 2. The kinetic energy release values calculated from analysis of the peak associated with CH Cl 2 - in the charge-inversion mass spectrum of the parent CH 2 Cl 2 + ion indicate that the excited CH 2Cl 2 formed by neutralization dissociates spontaneously into CHCl 2 + H.

Double- and single-electron transfer inH++Kcollisions from0.3to4keV: Separation of direct double transfer and two-step successive single-electron transfer

Double-electron transfer and two-step single-electron transfer in collisions of proton with potassium-metal target are measured in the collision energy from 0.3 to 4 keV by using a charge-inversion mass spectrometry. Two prominent H{sup -} ion peaks are observed with different values of the energy loss and show different target density dependences. The peak with larger energy loss is identified as double-electron transfer and the other as two-step successive single-electron transfer from the analysis of the target density dependence. The two-step single-electron transfer is considered to occur as the process accompanying spontaneous Ly-{alpha} emission, followed by negative H{sup -} formation. A theoretical analysis is also carried out, and the single-electron transfer cross section obtained is found to be in excellent agreement with the present measurement, while the present measurement for double-electron transfer is found to be much smaller than those evaluated earlier and the present theory.

A new technique to study the dissociation of energy-selected neutral intermediates

The dissociation of excited species is one of the most important types of chemical reactions, and it has been investigated by using either molecular collision or photon excitation. Mass spectrometry is suited to generate and probe unstable intermediates in the gas phase and has enabled the investigation of the dissociation of various stable and unstable ions. However, investigation of neutral species using this technique has been difficult because of their lack of electronic charge. In this work we have used mass spectrometry to measure collision-induced dissociation (CID) spectra and charge-inversion spectra of CD 3OH + and CH 3OD +. The major dissociation process in CID was found to involve elimination of a hydrogen atom from the methyl group, whereas dissociation in the charge-inversion mass spectrometer was found to be via elimination of a hydrogen atom from the hydroxyl group. Hydrogen atom elimination from the hydroxyl group has also been reported as the major process in the photo-induced dissociation of neutral methanol. This demonstrates the usefulness of charge-inversion mass spectrometry as a technique for the investigation of the dissociation of neutral intermediates.

Sequential electron capture reactions and state compositions of beams of first-row diatomic cations

Charge-inversion mass spectroscopy has been used to study fast beams of O+2, NO+, CF+, CH+, NH+ and CN+ cations formed from given precursor molecules under 100 eV electron impact. Beams of O+2 and NO+ formed from the respective gases, and CF+ formed from CF4, were found to contain 0.48+or-0.05, 0.45+or-0.06 and 0.38+or-0.08 proportions of metastable ions. In contrast, NO+ ions formed from nitromethane, and CF+ ions from CHF3, were almost entirely in their ground states. Significant but indeterminable proportions of 3 Pi -state ions were found in beams of CH+ ions formed from C2H2 and CH4 while the beam of NH+ ions formed from NH3 has been estimated to contain at least 25% of excited 4 Sigma - ions. Beams of CN+ ions formed from CH2H2, HCN and nitromethane gave spectra that suggest the presence of a large proportion of electronically excited cations, possibly in vibrationally hot levels of the 3 Pi state. All spectra are discussed in the light of these state distributions and with regard to the ergicities and Franck-Condon factors for the single electron capture reactions involved.

A reaction window in double charge-transfer mass spectrometry

Endoergic ion/molecule reactions resulting in double electron capture are analysed within a simple curve-crossing model. A Landau-Zener-type treatment indicates the existence of a reaction window in the functional dependence of the double charge-transfer cross-section on the endoergicity of the overall process. Practical implications for charge-inversion mass spectrometry are discussed.