Evaluation of the computational methods for electron-impact total ionization cross sections: Fluoromethanes as benchmarks

Electron Scattering from 1-Methyl-5-Nitroimidazole: Cross-Sections for Modeling Electron Transport through Potential Radiosensitizers

In this study, we present a complete set of electron scattering cross-sections from 1-Methyl-5-Nitroimidazole (1M5NI) molecules for impact energies ranging from 0.1 to 1000 eV. This information is relevant to evaluate the potential role of 1M5NI as a molecular radiosensitizers. The total electron scattering cross-sections (TCS) that we previously measured with a magnetically confined electron transmission apparatus were considered as the reference values for the present analysis. Elastic scattering cross-sections were calculated by means of two different schemes: The Schwinger multichannel (SMC) method for the lower energies (below 15 eV) and the independent atom model-based screening-corrected additivity rule with interferences (IAM-SCARI) for higher energies (above 15 eV). The latter was also applied to calculate the total ionization cross-sections, which were complemented with experimental values of the induced cationic fragmentation by electron impact. Double differential ionization cross-sections were measured with a reaction microscope multi-particle coincidence spectrometer. Using a momentum imaging spectrometer, direct measurements of the anion fragment yields and kinetic energies by the dissociative electron attachment are also presented. Cross-sections for the other inelastic channels were derived with a self-consistent procedure by sampling their values at a given energy to ensure that the sum of the cross-sections of all the scattering processes available at that energy coincides with the corresponding TCS. This cross-section data set is ready to be used for modelling electron-induced radiation damage at the molecular level to biologically relevant media containing 1M5NI as a potential radiosensitizer. Nonetheless, a proper evaluation of its radiosensitizing effects would require further radiobiological experiments.

Evaluation of electron ionization cross-sections of methyl halides

RATIONALE

Electron collision with methyl halides CH(3)X (X  =  F, Cl, Br) plays an important role in various atmospheric and plasma modelling processes. The gaseous methyl halides are harmful to the troposphere and the stratospheric ozone layer. Knowledge of the ionization cross sections and ionization rate coefficients of the free gaseous halides is therefore desirable in the study of these processes.

METHODS

The partial single and double differential cross-sections with the integral ionization cross-sections of the gaseous halides by electron collision were calculated using a modified Jain-Khare semi-empirical approach. The ionization rate coefficients corresponding to partial ionization cross-sections were calculated by the Maxwell-Boltzmann distribution of energy.

RESULTS

The Jain-Khare formalism has different approaches for the evaluation of single differential, double differential and integral ionization cross-sections. The partial single differential cross-sections as a function of energy loss (sum of ionization threshold and the secondary electron energy) suffered by the incident electron were calculated at incident electron energies of 100 and 200 eV. The double differential cross-sections were computed at the same electron energies and scattering angles of 30° and 60°. The behavior of double differential cross-sections with scattering angles from 0° to 180° at constant secondary electron energies of 10 and 20 eV and fixed primary electron energies 100 and 200 eV was also calculated. The partial and total (sum of all partial cross-sections) integral ionization cross-sections were evaluated from the ionization threshold to 1000 eV.

CONCLUSIONS

The applied formalism is useful for the calculation of partial and total integral/or differential cross-sections at low energies. The integral ionization cross-sections showed good agreement with available experimental/or theoretical data. The data obtained for these compounds were not previously available, so the results will be of value to the experimental and theoretical community concerned with plasma and atmospheric processes.

Molecular basic data calculation for radiation transport in chromatin

Differential and integral electron impact ionisation cross sections were calculated using the binary-encounter-Bethe theoretical model for each core particle molecules: the four DNA bases, the backbone (sugar phosphate), and the 19 amino acids constituent of histone proteins. The binding energies and populations of molecular orbitals were computed using General Atomic Molecular Electronic Structure System. At present, there are neither experimental nor other theoretical results on amino acid electron impact ionisation cross sections. Regarding DNA bases and backbone, our results show good agreement with those published in journals.

Absolute electron-impact total ionization cross sections of chlorofluoromethanes

An experimental study is reported on the electron-impact total ionization cross sections (TICSs) of CCl4, CCl3F, CCl2F2, and CClF3 molecules. The kinetic energy of the colliding electrons was in the 10-85 eV range. TICSs were obtained as the sum of the partial ionization cross sections of all fragment ions, measured and identified in a linear double focusing time-of-flight mass spectrometer. The resulting TICS profiles--as a function of the electron-impact energy--have been compared both with those computed by ab initio and (semi)empirical methods and with the available experimental data. The computational methods used include the binary-encounter-Bethe (BEB) modified to include atoms with principal quantum numbers n> or =3, the Deutsch and Märk (DM) formalism, and the modified additivity rule (MAR). It is concluded that both modified BEB and DM methods fit the experimental TICS for (CF4), CClF3, CCl2F2, CCl3F, and CCl4 to a high accuracy, in contrast with the poor accord of the MAR method. A discussion on the factors influencing the discrepancies of the fittings is presented.