Coulomb explosion of ions produced by electron impact ionization of toluene (original) (raw)
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Electron impact ionization cross-sections of toluene
Chemical Physics Letters, 2007
Electron impact ionization of toluene is studied using mass spectrometry. Cross-sections for the formation of molecular ions and ionic fragments are measured between 10 and 78 eV with a total cross-section of 1:5 Â 10 À15 cm 2 towards 60 eV. C 7 H þ 8 and C 7 H þ 7 contribute to 75% of the total cross-section at 78 eV. The molecular ion is the most abundant below 25 eV. Four ionic fragments: C 5 H þ 5 ; C 4 H þ 3 ; C 5 H þ 3 and C 3 H þ 3 , are detected above 20 eV. Enthalpy considerations can lead to think that C 5 H þ 5 is issued directly from the molecular ion, whereas the three other species result from two step pathways.
Ion-induced molecular fragmentation: beyond the Coulomb explosion picture
Journal of Physics B: Atomic, Molecular and Optical Physics, 2000
The fragmentation of the CO molecule by O 7+ ion impact is investigated in two different energy regimes by fragment ion momentum spectroscopy. The improved resolution of the present kinetic energy release measurement together with application of a time-dependent wavepacket dynamics method used in conjunction with new high-level computations of a large number of dication potential energy curves enables one to unambiguously assign each line to an excited state of the transient molecular dication produced during the collision. This is the first direct experimental evidence of the limitations of the Coulomb explosion model to reproduce the molecular fragmentation dynamics induced by ion impact. Electron removal due to a capture process is shown to transfer less excitation to the target than direct ionization. At low collision velocity, the three-body interaction between the projectile and the two fragments is also clearly highlighted.
Journal of Physics B Atomic Molecular and Optical Physics
Absolute cross sections for electron-impact single ionization, dissociative excitation and dissociative ionization of the ethynyl radical ion (C2D + ) have been measured for electron energies ranging from the corresponding reaction thresholds to 2.5 keV. The animated crossed electron-ion beam experiment is used and results have been obtained for the production of C2D 2+ , C 2+ , C + 2 , CD + , C + and D + . The maximum of the cross section for single ionization is found to be (2.01 ± 0.02) × 10 −17 cm 2 , at the incident electron energy of 105 eV. Absolute total cross sections for the various singly charged fragments production are observed to decrease by a factor of almost three, from the largest cross-section measured for C + , over C + 2 and CD + down to that of D + . The maxima of the cross sections are obtained to be (14.5 ± 0.5) × 10 −17 cm 2 for C + 2 , (12.1 ± 0.1) × 10 −17 cm 2 for CD + , (27.7 ± 0.2) × 10 −17 cm 2 for C + and (11.1 ± 0.8) × 10 −17 cm 2 for D + . The smallest cross section is measured to be (1.50 ± 0.04) × 10 −18 cm 2 for the production of the doubly charged ion C 2+ . Individual contributions for dissociative excitation and dissociative ionization are determined for each singly-charged product. The cross sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. Kinetic energy release distributions of dissociation fragments are seen to extend from 0 to 6 eV for the heaviest fragment C + 2 , up to 11.0 eV for CD + , 14.2 eV for C + and 11.2 eV for D + products.
Cross sections and ion kinetic energy analysis for the electron impact ionization of acetylene
The Journal of Chemical Physics, 2006
Using a Nier-type electron impact ion source in combination with a double focusing two sector field mass spectrometer, partial cross sections for electron impact ionization of acetylene are measured for electron energies up to 1000eV. Discrimination factors for ions are determined using the deflection field method in combination with a three-dimensional ion trajectory simulation of ions produced in the ion source. Analysis of the ion yield curves obtained by scanning the deflectors allows the assignment of ions with the same mass-to-charge ratio to specific production channels on the basis of their different kinetic energy distributions. This analysis also allows to determine, besides kinetic energy distributions of fragment ions, partial cross sections differential in kinetic energy. Moreover a charge separation reaction, the Coulomb explosion of the doubly charged parent ions C2H2++ into the fragment ions C2H+ and H+, is investigated and its mean kinetic energy release (⟨KER⟩=3.88...
III. Electron-impact dissociative ionization of C2H 2 + and C2D 2 +
The European Physical Journal D, 2010
Absolute cross-sections for electron-impact dissociative ionization of C2H + 2 and C2D + 2 to CH + , C + , C + 2 , H + , CH + 2 and C2D + fragments are determined for electron energies ranging from the corresponding threshold to 2.5 keV. Results obtained in a crossed beams experiment are analyzed to estimate the contribution of dissociative ionization to each fragment formation. The dissociative ionization cross sections are seen to decrease for more than an order of magnitude, from CH + (5.37 ± 0.10) × 10 −17 cm 2 over C + (4.19 ± 0.16) × 10 −17 cm 2 , C2D + (3.94 ± 0.38) × 10 −17 cm 2 , C + 2 (3.82 ± 0.15) × 10 −17 cm 2 and H + (3.37 ± 0.21) × 10 −17 cm 2 to CH + 2 (2.66 ± 0.14) × 10 −18 cm 2 . Kinetic energy release distributions of fragment ions are also determined from the analysis of the product velocity distribution. Cross section values, threshold energies and kinetic energies are compared with the data available from the literature. Conforming to the scheme used in the study of the dissociative excitation of C2H + 2 C2D + 2 , the cross-sections are presented in a format suitable for their implementation in plasma simulation codes.
2022
We report on the fragmentation dynamics of triply charged, diatomic, molecular ions of NO and CO. Dissociative fragmentation after multiple ionization of NO and CO is studied under the impact of 200 keV proton beam using recoil-ion momentum spectrometer. Kinetic Energy Release distributions (KERDs) for various fragmentation channels were obtained. We have also calculated the potential energy curves (PECs) for ground and several excited states of NO^{3+} and CO^{3+} molecular ion. The obtained KERDs are discussed in the background of the calculated PECs as well as the simple Coulomb excitation model. Coulomb breakup of the unstable precursor molecular ion shows a clear preference for the N^{2+} + O^+ (and C^{2+} + O^+) fragmentation channel.
Electron-impact ionization and dissociation of C2D+
The European Physical Journal D, 2010
Absolute cross sections for electron-impact single ionization, dissociative excitation and dissociative ionization of the ethynyl radical ion (C2D +) have been measured for electron energies ranging from the corresponding reaction thresholds to 2.5 keV. The animated crossed electron-ion beam experiment is used and results have been obtained for the production of C2D 2+ , C 2+ , C + 2 , CD + , C + and D +. The maximum of the cross section for single ionization is found to be (2.01 ± 0.02) × 10 −17 cm 2 , at the incident electron energy of 105 eV. Absolute total cross sections for the various singly charged fragments production are observed to decrease by a factor of almost three, from the largest cross-section measured for C + , over C + 2 and CD + down to that of D +. The maxima of the cross sections are obtained to be (14.5 ± 0.5) × 10 −17 cm 2 for C + 2 , (12.1 ± 0.1) × 10 −17 cm 2 for CD + , (27.7 ± 0.2) × 10 −17 cm 2 for C + and (11.1 ± 0.8) × 10 −17 cm 2 for D +. The smallest cross section is measured to be (1.50 ± 0.04) × 10 −18 cm 2 for the production of the doubly charged ion C 2+. Individual contributions for dissociative excitation and dissociative ionization are determined for each singly-charged product. The cross sections are presented in closed analytic forms convenient for implementation in plasma simulation codes. Kinetic energy release distributions of dissociation fragments are seen to extend from 0 to 6 eV for the heaviest fragment C + 2 , up to 11.0 eV for CD + , 14.2 eV for C + and 11.2 eV for D + products.
Dissociation of alkane ionized molecules
Technical Physics, 2010
The subject of investigation is the fragmentation of variously charged molecular ions arising in col lisions of several kiloelectronvolt H + , He 2+ , and Ar 6+ ions with molecules of the simplest alkanes (from meth ane to butane). Using the method of time of flight mass spectrometry, the formation cross sections of disso ciation induced fragment ions are measured. The dissociation takes place when an incident ion captures an electron from a methane, ethane, or propane molecule. The role of additional ionization of the molecule, which accompanies the electron capture by the incident ion, is elucidated. The kinetic energy spectrum for protons resulting from the fragmentation of multiply charged alkane ions is determined. The most plausible kinetic energies of protons depending on the degree of ionization and molecule size fall into the range 1-25 eV. It is shown that, when the molecule loses several electrons, the kinetic energies of protons are governed by Coulomb interaction between all fragment ions and are determined by their flying apart from the relative spa tial arrangement of corresponding atoms in a parent molecule.
Fragmentation of three isotopic toluene monocations in the 15–100 eV photon energy range
Chemical Physics, 1999
The dissociative photoionization of toluene-h , toluene-a-d and toluene-d was studied within the 15-100 eV photon 8 3 8 energy range using monochromatized synchrotron radiation as excitation source and a reflectron time-of-flight mass spectrometer in both electrostatic mirror and linear modes. Peak profile analyses of the linear mode spectra provided information on the kinetic energy release and, in some cases, the percentage of mono-to dication dissociations leading to the formation of particular ion fragments. Supporting data from photoelectron-photoion-photoion coincidence measurements on toluene-h at 100 eV were used to detail the contributing dication charge separation processes at high excitation energies. Fragment ion formation threshold energies, obtained from photoion mass spectrometry measurements, were used to determine possible fragmentation pathways on the basis of reaction thermochemistry. Where competitive reaction channels are possible, use was made of energy propensity rules, involving product ionization potentials and proton affinities, to propose favored pathways. Previously limited to a maximum of 20 eV photon energy and to studies of only two fragments, C H q and C H q , our results extend the data on dissociative photoionization processes of toluene to 100 eV and to ) 40 7 7 5 5 ) Corresponding
Chemical Physics Letters, 2005
Kinetic energy distributions and yields of the ions produced in the electron impact ionization of methyl tert-butyl ether (MTBE) have been measured by TOF mass spectrometry. The detection efficiency as a function of the initial ion kinetic energy has been carefully evaluated by means of a Montecarlo simulation of the experimental conditions. The resulting kinetic energy spectra show that almost all the heaviest ions are produced with quasi-thermal energy distribution, while the smaller fragment ions H + and CH þ 3 exhibit in addition substantial non-thermal components. As a final result, the total ionization cross-section of MTBE in the range 20-150 eV of the ionizing-electron energy has been derived and calibrated against the argon, chosen as a reference gas.