Processes Involving Electrons with Khimera
Quantitative data on cross sections and rate constants of processes with the participation of electrons are of great importance for kinetic modeling in gas discharge, lighting, gaseous lasers, plasma chemistry, and plasma processing.
Model approaches to evaluating the cross sections and rate constants of processes involving electrons are based on qualitative physical ideas about the mechanisms of interaction between the incident electron and the atomic or molecular target. The elastic scattering, dissociation, and excitation processes are treated within the framework of the Born approximation, corrected by taking into account the set of available experimental data. The processes performed through the formation of a temporary compound are processed within the framework of the Breit–Wigner model using quantum chemical data on the width of the relevant state.
Example: electron impact ionization of Te
The process Te + e → Te+ + e + e plays an important role in plasma chemical technology of semiconductor electronics. The cross section of this process is calculated within the frame of Born-Compton approximation, that has manifested itself quite well in evaluation of the ionization cross section for elements with a moderate value of the ionization potential. This approach is distinguished in its simplicity and requires a few data on the atom under investigation.
The window of the Khimera module with the results of calculations of the ionization cross section for Te is presented in the picture along with the available experimental data.
Example: electron impact excitation of Mg (3s1So-3p1P1)
Electron impact excitation of optically allowed states of atoms determines the emission and electrical properties of low-temperature plasmas. The cross section of this process is determined within the framework of the modified Born approximation using the similarity function method. This approach requires knowledge of the oscillator strength and the energy of the transition under consideration. The figure below compares the results of calculations of the excitation cross section with the available experimental data. It is seen that the similarity function method provides quantitative agreement with experiment and can be used as a tool of high predictability.
Example: electron impact dissociation of SF molecule
The process of the electron impact dissociation of molecules is one of the main mechanisms of initial chemical transformation in chemically active plasma. Specifically, the dissociation of an SF molecule determines the kinetics of plasma etching in semiconductor production. The cross section of this process is calculated within the framework of the similarity function method using the results of quantum chemical calculations of the potential energy curves for both the ground and excited states of the molecule, as well as the dependence of the transition dipole moment on the internuclear distance. The dissociation process proceeds through the formation of a repulsing state on the molecule.
