Mechanisms of single-electron capture by the dichlorocarbene dication

Abstract

The single-electron capture (SEC) by dichlorocarbene dications with eight different atomic and molecular target gases, CCl 2 (2+) + G → CCl 2 (+) + G(+), has been studied by product ion spectroscopy and ion kinetic energy spectroscopy. The experimental data have been interpreted in the framework of a theoretical model mat describes the charge exchange process. Exothermic charge exchange is handled within the Landau-Zener model, whereas endothermic charge exchange is described by the Demkov model. The calculated data reproduce qualitatively the essential features of the experimental results: (1) the appearance of a reaction window centered at an exothermicity in the 4-4.5-eV range, (2) the lower SEC cross sections for endothermic charge exchange, (3) the wider internal energy distributions obtained for CCl 2 (+) in the endothermic regime than in the exothermic one, which results in larger dissociation yields, (4) the excitation of molecular targets that accompany their ionization in the SEC process, and (5) the kinetic energy released on the CCl(+) + Cl fragments in dissociative SEC.

Charge Exchange in Tandem Mass Spectrometry: Dissociative Single Electron Capture by Doubly-Charged Toluene Cations

“…20 Molecular systems of medium size have, however, received much less attention. [21][22][23][24][25][26][27] In line with previous work, 15,27 we will focus in this paper on a specific kind of collisional charge transfer, i.e. the single electron capture (SEC) between doubly-charged cations and various target gases at kiloelectronvolt collision energies.…”

“…These two factors can be evaluated by analysing translational ion spectra (V-scans) recorded under similar acceleration conditions as the spectra at constant B/E. 15 The translational energy spectrum resulting from the dissociation of a doubly-charged ion into two singlycharged fragments is dish-topped due to the large kinetic energy release associated with the Coulomb repulsive potential between the recoiling fragments. Much less kinetic energy is usually released on the [ion + neutral] fragments of a dissociating singly-charged ion resulting from single electron capture.…”

“…A reaction window has been evidenced for an exothermicity Q ≈ -4 to -5 eV. [10][11][12][13]15,27 Within this window, the charge transfer crosssection is maximal. If Q > 0, the potential energy surfaces do not cross when the collision partners get close to each other and the Demkov model 42,43,49 is more appropriate.…”

“…These reactions involve, by their very definition, the nuclear coupling between at least two electronic states that correlate with, respectively, the entrance and the exit reaction channels. Their detailed understanding remains, however, limited to atomic or small molecular systems (di-and triatomics), [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] where very detailed experiments can be performed and compared to sophisticated calculations even involving, recently, wave packet propagations. 20 Molecular systems of medium size have, however, received much less attention.…”

“…The observed shape for the cross-section illustrates once again the reaction window concept. [10][11][12][13]15,27 This concept derives from the fact that the optimal transition probability depends on the position of the crossing point between the diabatic potential energy curves, which in turn is determined by the exothermicity of the reaction 44 [see Figure 2 and Equation (8)].…”