Electron impact ionization cross-sections of toluene (original) (raw)
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Coulomb explosion of ions produced by electron impact ionization of toluene
Vacuum, 2005
Doubly charged C 7 H 2þ 7 ions produced by electron impact ionization of toluene (C 7 H 8) show metastable unimolecular dissociation into two singly charged fragments. A high-resolution double focusing mass spectrometer (reversed Nier-Johnson type BE geometry) was used to monitor these decomposition reactions. We have identified four competing charge separation channels. The mass-analyzed ion kinetic energy (MIKE) technique was used to determine mean values of the kinetic energy release (KER). We obtained values of the average KER for the charge separation reactions of C 7 H 2þ 7 ranging from 2.5 to 3.5 eV.
Evaluation of Electron-Impact Ionization Cross Sections for Molecules
Journal of Physical Chemistry A, 2019
We describe the recent progress in the development of the semi-empirical approach developed by Jain and Khare for the calculations of ionization cross sections for molecules by electron impact. Along with the state-of-the-art description of this approach, the emphasis will be on the evaluation of cross sections for carbon dimer C 2 and trimer C 3 .
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
The Journal of Physical Chemistry a, 2011
The experimental determination of absolute total electron impact ionization cross-sections for polyatomic molecules has traditionally been a difficult task and restricted to a small range of species. This article reviews the performance of three models to estimate the maximum ionization cross-sections of some 65 polyatomic organic and halocarbon species. Cross-sections for all of the species studied have been measured experimentally using the same instrument, providing a complete data set for comparison with the model predictions. The three models studied are the empirical correlation between maximum ionization cross-section and molecular polarizability, the well-known binary encounter Bethe (BEB) model, and the functional group additivity model. The excellent agreement with experiment found for all three models, provided that calculated electronic structure parameters of suitably high quality are used for the first two, allows the prediction of total electron-impact ionization cross-sections to at least 7% precision for similar molecules that have not been experimentally characterized.
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...
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.
Electron-impact ionization cross sections of atmospheric molecules
The Journal of Chemical Physics, 1997
A theoretical model for electron-impact total ionization cross sections, which has been found to be reliable for a wide range of molecules, is applied to molecules of interest to atmospheric science. The new theory, the binary-encounter-Bethe ͑BEB͒ model, combines the binary-encounter theory and the Bethe theory for electron-impact ionization, and uses simple theoretical data for the ground state of the target molecule, which are readily available from molecular structure codes. Total ionization cross sections of 11 molecules, CS, CS 2 , COS, CH 4 , H 2 S, NH 3 , NO 2 , N 2 O, O 3 , S 2 , and SO 2 , are presented for incident electron energies from threshold to 1 keV with an average accuracy of 15% or better at the cross section peak. We also found that the use of vertical ionization potentials ͑IPs͒ rather than adiabatic IPs for the lowest IPs significantly improves BEB cross sections between the threshold and cross section peak for molecules whose adiabatic and vertical IPs are different by ϳ1 eV or more ͑CH 4 and NH 3). The BEB cross sections are presented in a compact analytic form with a small number of constants, making the cross sections suitable for modeling applications.
Atoms
The electron impact partial ionization cross-sections of molecules such as methane, water and nitromethane are computed using a modified form of the binary encounter Bethe (BEB) formula. The modified form of the BEB model works on rescaling the molecular binding energies of the orbitals and the scaling of cross-sections using the electron ionization mass spectrometry data. The computed partial ionization cross-sections are consistent with the recommended data and are better than several experimental and theoretical results. The summed partial ionization cross-sections of different fragments also agree with the total ionization cross-sections obtained from BEB and the experimental data. This work highlights the utility of mass spectrometry in the modeling and interpretation of the ionization cross-section data. The limitations and the advantages of the modified form of the BEB model are also discussed.