Electron impact dissociative ionization of CO2: Measurements with a focusing time-of-flight mass spectrometer

Abstract

For reliable cross section data a focusing time-of-flight mass spectrometer has been presented which collects all the ions produced by the electron impact dissociative ionization of molecules. The focusing characteristic of the mass spectrometer generates the ions close to the axis and focuses the energetic ions back to the detector. By observing the deflection curves we can measure the cross sections conclusively. The complete collection allows one to extract the initial kinetic energy distribution of the ions from the time-of-flight profiles of the mass peaks. As a first example we measured the cross sections of electron impact dissociative ionization of CO2 for electron energies from threshold to 300 eV. The results agree very well with recent measurements of Straub et al. [J. Chem. Phys. 105, 4015 (1996)], although previous data are in very poor agreement with each other. We measured the initial translational energy distribution of the fragment ions from the dissociative ionization of CO2 . With respect to the kinetic energy distribution of the ions we analyzed the techniques which make use of the quadrupole mass spectrometer. We discuss why the results from the quadrupole mass spectrometer underestimate the cross sections for the fragment ions. Finally we suggest to recheck the data from earlier quadrupole mass spectrometer measurements.

Electron ionization of CO2

“…In this article, we report relative PICS σ r [X m+ ] for the formation of C + , O + , CO + , C 2+ , O 2+ and CO 2 2+ ions. This data is shown to be in excellent agreement with the existing PICS of Straub et al [14] and Tian and Vidal [16]. We then present precursor-specific relative PICS σ n [X m+ ], which, as shown by our recent studies of the electron ionization of C 2 H 2 [30] and N 2 O [31], quantify the contribution to the yield of a fragment ion from single (n = 1), double (n = 2) and triple (n = 3) ionization.…”

“…In this way Straub et al [14] were able to demonstrate the complete collection of all ionic fragments, including those formed with considerable translational kinetic energy. Tian and Vidal [16] used a focusing time-of-flight mass spectrometer to measure PICS up to an electron energy of 300 eV and cross-sections for the formation of ion pairs up to 600 eV using a covariance mapping technique [15]. Comparison of these more recent determinations to the existing PICS data sets revealed some considerable discrepancies, particularly concerning the formation of the fragment ions C + and O + , for which the PICS values of Straub et al [14] and Tian and Vidal [16] are considerably larger than those measured in previous studies.…”

“…The dissociative ionization of CO 2 has been the subject of a number of investigations employing a variety of techniques: electron-ionization mass spectrometry [4][5][6][7][8][9][10][11][12][13][14][15][16][17], photoionization mass spectrometry [18][19][20][21][22][23][24][25], collisions with positrons [26], collisions with high translational energy ions [27], ultrafast laser pulses [28] and coincidence techniques [19][20][21][23][24][25]27,29,28]. Concentrating on the previous cross determinations for electron ionization of CO 2 , the total ionization cross section has been measured from threshold to 100 eV by Asundi et al [4] and from threshold to 1000 eV by Rapp and Englander-Golden [5].…”

Analytic Cross Sections for Electron Collisions With Co, Co2, and H2o Relevant to Edge Plasma Impurities

“…The experimental uncertainty is estimated to be ±10%. A similar measurement was performed by Tian and Vidal [49] in the energy range up to 300 eV. The two sets of results are in good agreement.…”

Exospheres and Atmospheric Escape

“…Fox and Dalgarno (1979) concluded that in electron impact dissociation of CO 2 the mean energy released was ∼ 1 eV. Dissociative ionization, processes (12) and (14), are known to produce very energetic products (e.g., Locht and Davister 1995;Tian and Vidal 1998). The energetic ions and neutrals are mostly due to predissociation of electronically excited states of the ions.…”