Total Electron Ionization Cross Sections Research Articles

(e,2e) ionization cross-sections for C4H4O, C4H8O and C6H8O

Secondary electron energy dependent differential cross-sections at incident electron energies 100 and 200 eV for (e, 2e) processes for the C4H4O, C4H8O and C6H8O molecules are evaluated by employing the Jain-Khare semi-empirical approach. The total electron ionization cross sections in the incident electron energy range ionization threshold to 5 keV are derived from energy dependent cross sections. The ionization rate coefficients for molecules are also calculated using the total ionization cross sections and the Boltzmann distribution of electron energies. The present results for ionization cross sections corresponding to (e, 2e) processes for these molecules are found in good agreement with available experimental and theoretical results.

Electron ionization of the CN+ molecule

We present electron ionization cross sections for the CN+ molecule. A configuration-average distorted-wave method is used to compute the electron ionization cross sections based on earlier molecular structure tabulations. Electron ionization cross sections are calculated for the outer 4 subshells of the 1σ22σ23σ24σ21π25σ2 ground configuration and for the outer 3 subshells of the 1σ2 2σ23σ24σ21π4 excited configuration. The total electron ionization cross sections are compared with recent total crossed-beams measurements that include production of CN2+, C+, C2+, N+, and N2+. The total theoretical and experimental cross sections are in fairly good agreement, especially at the higher electron energies.

Total electron ionization cross-sections for molecules of astrochemical interest

ABSTRACTWe describe a newly upgraded instrument for measuring absolute total electron ionization cross-sections over the energy range from 0 to 300 eV, and present cross-sections for nine previously unstudied molecules, as well as several small molecules for which comparison data is available. The measured cross-sections are compared with the predictions of the BEB model, and show reasonable agreement with the model, albeit peaking at higher electron energies than predicted by the model. We show that the maxima in the cross-sections follow an additivity model, such that the molecular cross-sections can be expressed as a sum over contributions from the constituent atoms. These contributions have been determined from a global fit to the data for all molecules studied, and allow maximum cross-sections to be predicted for molecules that have not been studied to date. We demonstrate the expected correlation between the maximum ionization cross-section and the molecular polarisability, and show that the atomic contributions to the cross-section show a similar dependence on the atomic polarisability. The observed correlation can be used as an alternative method for predicting unknown maximum cross-sections.

Communication: Electron ionization of DNA bases.

No reliable experimental data exist for the partial and total electron ionization cross sections for DNA bases, which are very crucial for modeling radiation damage in genetic material of living cell. We have measured a complete set of absolute partial electron ionization cross sections up to 500 eV for DNA bases for the first time by using the relative flow technique. These partial cross sections are summed to obtain total ion cross sections for all the four bases and are compared with the existing theoretical calculations and the only set of measured absolute cross sections. Our measurements clearly resolve the existing discrepancy between the theoretical and experimental results, thereby providing for the first time reliable numbers for partial and total ion cross sections for these molecules. The results on fragmentation analysis of adenine supports the theory of its formation in space.

Absolute partial and total electron ionization cross sections of uracil

Absolute partial and total electron ionization cross sections for uracil in the gas phase as a function of energy up to 500eV are measured using the well-known relative flow technique (RFT). These measurements have significant consequences for the study of radiation damage, tests of several theoretical models and application of the RFT for molecules existing in solid form at room temperature. Also presented are the thresholds for the formation of various fragment ions from uracil and the comparison of total ionization cross section with the existing results.

Absolute Electron Ionization cross sections for Cytosine

SynopsisAbsolute partial and total electron ionization cross sections for the DNA base Cytosine are measured using Relative Flow Technique (RFT) up to 500 eV.

Collision dynamics of proton with formaldehyde: Fragmentation and ionization

Using time-dependent density functional theory, applied to the valence electrons and coupled non-adiabatically to molecular dynamics of the ions, we study the ionization and fragmentation of formaldehyde in collision with a proton. Four different impact energies: 35 eV, 85 eV, 135 eV, and 300 eV are chosen in order to study the energy effect in the low energy region, and ten different incident orientations at 85 eV are considered for investigating the steric effect. Fragmentation ratios, single, double, and total electron ionization cross sections are calculated. For large impact parameters, these results are close to zero irrespective of the incident orientations due to a weak projectile-target interaction. For small impact parameters, the results strongly depend on the collision energy and orientation. We also give the kinetic energy releases and scattering angles of protons, as well as the cross section of different ion fragments and the corresponding reaction channels.

Absolute partial and total electron ionization cross sections for CCl4 from threshold up to 180 eV

Electron impact ionization of carbon tetrachloride was studied as a function of electron energy from threshold up to 180 eV. A double-focusing mass spectrometer system in combination with an improved electron impact ion source was used, alleviating the problems of ion extraction from the source and the transmission of the extracted ions through the mass spectrometer system. Absolute partial ionization cross sections for the occurrence of CCl3+, CCl2+, CCl+, Cl2+, Cl+, C+, CCl32+, and CCl22+ have been determined. In addition, the total ionization cross-section function of CCl4 is reported and compared with theoretical predictions based on a classical binary encounter approximation. Using nth root extrapolation the following ionization energies of the doubly ionized fragment ions have been derived: AE(CCl32+)=30.4±0.3 eV; and AE (CCl22+)=31.8±0.3 eV. In accordance with theoretical predictions and previous results, no stable CCl4+ has been detected, however, metastable dissociation processes CCl4+ → CCl3+ have been observed.