The Reactions Framework surpasses previous interaction frameworks in both speed and flexibility in types of processes that can be added to simulations. See Reactions Text-Setup Introduction, as well as relevant sections in the VSim User Guide for more general information on the Reaction framework.
The Reaction framework collisions are available when particles in the Basic Settings element
is set to include particles and the collision framework is set to reactions. This will add a “Reactions”
element to appear within the “Particle Dynamics” element.
When a collision process is added to a simulation, the user must specify each of the products and reactants from the drop down menus corresponding to each species in the chemical formula. Additionally, users must add a cross-sections to determine the reaction probability as to determine how many particles to react with in each cell for each timestep. Scroll to the bottom of this page for the reference on setting cross-sections.
These collisions are for interactions between kinetically modeled particle species (for a process involving a background gas use the “Particle Fluid Collisions”). The following interactions are available by right-clicking the “Particle Particle Collisions” element and hovering the mouse pointer over the “Add CollisionType” menu.
Charge Exchange A collision of the form \(A + B^+ \rightarrow A^+ + B\). This is the implementation of Charge Exchange in the visual setup.
The maximum energy lost during a single inelastic collision in eV. A choice of 0 (default) will give an elastic collision.
Impact Ionization
A collision of the form \(A + B \rightarrow A^+ + B + e\). This is the implementation of Impact Ionization
in the visual setup. If one of the reactant species is an electron, the Electron Ionization productGenerator
is used. Ionization energies are taken from the appropriate species blocks.
Note
If an electron is involved in an ionization process, the “product distribution” attribute won’t affect the simulation. The scattering distribution is determined automatically by a physical model.
Elastic A collision of the form \(A + B \rightarrow A + B\). This is the implementation of Binary Elastic in the visual setup.
The maximum energy lost during a single inelastic collision in eV. A choice of 0 (default) will give an elastic collision.
Dissociative Double Ionization A collision of the form \(AB + C \rightarrow A^+ + B^+ + C + 2e\). This is the implementation of Dissociative Ionization in the visual setup.
The energy required to dissociate the molecule, in eV. This value also sets a threshold for whether or not the reaction will occur. So a pair of particle will need at least this much relative energy (i.e. energy in center of momentum frame) in order to react. This can be set as a negative value to have the products gain kinetic energy.
Dissociative Single Ionization` A collision of the form \(AB + C \rightarrow A^+ + B + C + e\). This is the implementation of Dissociative Ionization in the visual setup.
The energy required to dissociate the molecule, in eV. This value also sets a threshold for whether or not the reaction will occur. So a pair of particle will need at least this much relative energy (i.e. energy in center of momentum frame) in order to react. This can be set as a negative value to have the products gain kinetic energy.
Dissociative Recombination A collision of the form \(AB^+ + e \rightarrow A + B\). This is the implementation of Dissociative Recombination in the visual setup.
The threshold energy for the reaction in eV. So, a pair of reactants will need at least this much relative energy (i.e. energy in center of momentum frame) in order to react. If the reaction occurs then this much energy is lost from the products to potential energy. If this is zero, then energy will not be lost. If negative, then the products will gain kinetic energy.
General Binary Reaction A collision of the form \(A + B \rightarrow C + D\). This is the implementation of Binary Reaction in the visual setup.
The threshold energy for the reaction in eV. So, a pair of reactants will need at least this much relative energy (i.e. energy in center of momentum frame) in order to react. If the reaction occurs then this much energy is lost from the products to potential energy. If this is zero, then energy will not be lost. If negative, then the products will gain kinetic energy.
Electron Impact Dissociation A collision of the form \(AB + e \rightarrow A + B + e\). This is the implementation of Electron Impact Dissociation in the visual setup.
The energy required to dissociate the molecule in eV.
Electron Attachment A collision of the form \(A + e \rightarrow A^-\). This is the implementation of Electron Attachment in the visual setup.
The threshold energy for the reaction in eV. So, a pair of reactants will need at least this much relative energy (ie energy in center of momentum frame) in order to react. If the reaction occurs then this much energy is lost.
Negative Ion Detachment A collision of the form \(A^- + B \rightarrow A + B + e\). The neutral reactant must be a kinetically modeled species. This is the implementation of Negative Ion Detachment in the visual setup.
The threshold energy for the reaction in eV. So, a pair of reactants will need at least this much relative energy (ie energy in center of momentum frame) in order to react. If the reaction occurs then this much energy is lost.
Excitation A collision of the form \(A + B \rightarrow A^* + B\). This is the implementation of Binary Excitation in the visual setup.
The potential energy, in eV, gained by the excited species (a positive value for this attribute will result in an energy loss from the simulation). This is also a threshold energy. The reaction will not occur between reactant that have a center of mass energy less than this value.
Inelastic Electron Scattering A collision of the form \(e + A \rightarrow e + A\). This is the implementation of Electron Scatter in the visual setup.
scatter type
- VahediSurendra Use the Vahedi-Surendra model to determine the scattering distrubution. See Electron Scatter for more information.
- isotropic Use an isotropic scattering distribution.
Recombination A collision of the form \(A^+ + e \rightarrow A\). This is the implementation of Binary Recombination in the visual setup, for the specific case of electron recombination.
These collisions are for interactions between kinetically modeled particle species and a background gas. The following interactions are available by right-clicking the “Particle Fluid Collisions” element and hovering the mouse pointer over the “Add CollisionType” menu.
Elastic A collision of the form \(A + B \rightarrow A + B\). This is the implementation of Binary Elastic in the visual setup.
The user can choose either fully elastic which conserves kinetic energy, or partially elastic
in which case the user
Charge Exchange A collision of the form \(A + B^+ \rightarrow A^+ + B\). This is the implementation of Charge Exchange in the visual setup.
The maximum energy lost during a single inelastic collision in eV. A choice of 0 (default) will give an elastic collision.
Impact Excitation A collision of the form \(A + B \rightarrow A^* + B\). This is the implementation of Binary Excitation in the visual setup.
The potential energy, in eV, gained by the excited species (a positive value for this attribute will result in an energy loss from the simulation). This is also a threshold energy. The reaction will not occur between reactant that have a center of mass energy less than this value.
Impact Ionization
A collision of the form \(A + B \rightarrow A^+ + B + e\). This is the implementation of Impact Ionization
in the visual setup. If one of the reactant species is an electron, the Electron Ionization productGenerator
is used. Ionization energies are taken from the appropriate species blocks.
Note
If an electron is involved in an ionization process, the “product distribution” attribute won’t affect the simulation. The scattering distribution is determined automatically by a physical model.
Electron Attachment A collision of the form \(A + e \rightarrow A^-\). This is the implementation of Electron Attachment in the visual setup.
The threshold energy for the reaction in eV. So, a pair of reactants will need at least this much relative energy (ie energy in center of momentum frame) in order to react. If the reaction occurs then this much energy is lost.
Negative Ion Detachment A collision of the form \(A^- + B \rightarrow A + B + e\). The neutral reactant must be a kinetically modeled species. This is the implementation of Negative Ion Detachment in the visual setup.
The threshold energy for the reaction in eV. So, a pair of reactants will need at least this much relative energy (ie energy in center of momentum frame) in order to react. If the reaction occurs then this much energy is lost.
Inelastic Scattering A collision of the form \(e + A \rightarrow e + A\). This is the implementation of Electron Scatter in the visual setup.
scatter type
- VahediSurendra Use the Vahedi-Surendra model to determine the scattering distrubution. See Electron Scatter for more information.
- isotropic Use an isotropic scattering distribution.
General Binary Reaction A collision of the form \(A + B \rightarrow C + D\). This is the implementation of Binary Reaction in the visual setup.
The threshold energy for the reaction in eV. So, a pair of reactants will need at least this much relative energy (i.e. energy in center of momentum frame) in order to react. If the reaction occurs then this much energy is lost from the products to potential energy. If this is zero, then energy will not be lost. If negative, then the products will gain kinetic energy.
Dissociative Double Ionization A collision of the form \(AB + C \rightarrow A^+ + B^+ + C + 2e\). This is the implementation of Dissociative Ionization in the visual setup.
The energy required to dissociate the molecule, in eV. This value also sets a threshold for whether or not the reaction will occur. So a pair of particle will need at least this much relative energy (i.e. energy in center of momentum frame) in order to react. This can be set as a negative value to have the products gain kinetic energy.
A collision of the form \(AB + C \rightarrow A^+ + B + C + e\). This is the implementation of Dissociative Ionization in the visual setup.
The energy required to dissociate the molecule, in eV. This value also sets a threshold for whether or not the reaction will occur. So a pair of particle will need at least this much relative energy (i.e. energy in center of momentum frame) in order to react. This can be set as a negative value to have the products gain kinetic energy.
The “Fluid Field” and “Particle Field” ionization processes both use Field Ionization
productGenerator. The distinction is made in the visual setup for benefit of the user.
Particle Field Ionization This is the implementation of Field Ionization for ionization of kinetically modeled particles by electric fields in the visual setup.
cross section type
- DCADK Use this when the time step resolves the oscillations of Electric field. See Field Ionization DCADK for more information.
- Average ADK Use this when the time step is much larger than the oscillations of Electric field. See Field Ionization Average ADK for more information.
Fluid Field Ionization This is the implementation of Field Ionization for ionization of background gases by electric fields in the visual setup.
cross section type
- DCADK Use this when the time step resolves the oscillations of Electric field. See Field Ionization DCADK for more information.
- Average ADK Use this when the time step is much larger than the oscillations of Electric field. See Field Ionization Average ADK for more information.
Decay This is the implementation of Decay in the visual setup
The lifetime (in seconds) of the unstable species.
Import cross sections from a data file with the independent variable (either velocity or energy) in the first column and the cross-section (dependent variable) in the second column. The imported file should NOT have any header.
velocity,
or energy.This can be used to set a user defined function for the cross section.
Use a cross section of the form \(Ax^E\). See Power Law Cross-Section for more information.
velocity,
or energy.The cross-sections will take the functional from of the equation:
where
See Exponential Polynomial Cross-Section for more information.
toZero parameter in the formula above.
Enter either “0” to have the cross-section go to zero at threshold,
or “1” to have the cross-section go to a non-zero value.Set the independent variable, x, in the equation above. Options are:
This sets how frequently the reaction is carried out. See the description of
updatePeriod in RxnProcessSettings Block for more information. The update
periodicity setting in the Visual Setup will set the updatePeriod when the
.sdf is translated to a .in file. Options are:
The reaction update will occur every timestep.
Set a custom update periodicity.
This will apply an anisotropy to the cross-section. See the section Anisotropy for more information. This attribute is only available for collisions with two reactant particles (or fluids) and two product particles (or fluids) except for the Inelastic Electron Scattering process which as the anisotropy set according to the Vahedi-Surendra model.
Add a preference for forward or backward scattering.