Syntax:
react_modify keyword values ...
recomb value = yes or no = enable or disable defined recombination reactions
rboost value = rfactor
rfactor = boost probability of recombination reactions by this factor
compute_chem_rates value = yes or no = enable or disable computation of Arrhenius rate for chemical
reaction without performing the reaction
partial_energy = yes or no = use partial energy or total energy for TCE chemistry
Examples:
react_modify recomb no react_modify rboost 100.0
Description:
Set parameters that affect how reactions are performed.
The recomb keyword turns on or off recombination reactions. It is only relevant if recombination reactions were defined in the reaction file read in by the react command. If the setting is no then they will be disabled even if they were listed in the reaction file. This is useful to turn recombination reactions off, to see if they affect simulation results.
The rboost keyword is a setting for recombination reactions. It is ignored if no recombination reactions exist, or the recomb keyword is set to no. The rboost setting does not affect the overalll statistical results of recombination reactions, but tries to improve their computational efficiency. Recombination reactions typically occur with very low probability, which means the code spends time testing for reactions that rarely occur. If the rfactor is set to N > 1, then recombination reactions are skipped N-1 out of N times, when one or more such reactions is defined for a pair of colliding particles. A random number us used to select on that probability. To compensate, when a recombination reaction is actually tested for occurrence, its rate is boosted by a factor of N, making it N times more likely to occur.
The smallest value rboost can be set to is 1.0, which effectively applies no boost factor.
IMPORTANT NOTE: Setting rboost too large could meant the probability of a recombination reaction becomes > 1.0, when it is does occur. SPARTA does not check for this, so you should estimate the largest boost factor that is safe to use for your model.
The compute_chem_rates keyword is a setting that allows the user to only compute Arrhenius rates for chemical reactions without performing them. Currently only the TCE reaction model supports this keyword; an error will occur when using the QK or TCE/QK reaction model with this keyword.
The partial_energy keyword is a setting that allows the user to choose the amount of internal energy and internal degrees of freedom used in the TCE model.
If the partial_energy keyword is set to yes, the rDOF model of Bird is used, and only the sum of the relative translational energy between the partcles and a fraction of the rotational energy is used. The participating internal degrees of freedom are either set to 1 (dissociation reactions), or 0 (recombination, exchange, ionization reactions).
Conversely, if the partial_energy keyword is set to no, then the total energy model is used, i.e. the sum of the relative translational energy between the partcles and the rotational and vibrational energies. The participating internal degrees of freedom are computed directly by the code and do not need to be inputted by the user. The vibrational energy model used has an impact on the internal degrees of freedom used in the TCE model in that case. This option is ignored for the QK reaction model.
Restrictions: none
Related commands:
Default:
The option defaults are recomb = yes, rboost = 1000.0, compute_chem_rates = no, partial_energy = yes.