Simulation

There is one of these objects for each simulation. The first one is for the main window, with others for each plot window. The settings can all be adjusted from the Constants window, and some can also be adjusted from menus in the main window and text boxes in the main window and plot windows.

Settings

IntensityUnits

Units for intensity. These are described in detail under Intensity Formulae. Possible values are:

Arbitrary - fastest, as it does not include the partition function, but can give misleading results (see below).
Normalized - default, and recommended for most cases unless absolute intensities are required.
Squared - square the calculated intensity
HonlLondon - The line strength factors, essentially the transition dipole moment summed over all the degenerate M levels and squared.
EinsteinASum - The Einstein A coefficient for each transition summed over upper and lower state M levels, with population factors excluded. This was EinsteinASum up to version 6.0.228.
EinsteinA - The Einstein A coefficient for each transition summed over lower state M levels, with population factors excluded. This corresponds to the radiative rate from the upper state.
nm2MHzperMolecule - for normal absorption
cm2WavenumberperMolecule - for normal absorption
HzperMolecule - for emission. This is the rate of emission of photons by one molecule on each transition, including the Boltzmann factor and partition function.
PopDist - for a time of flight spectrum or similar experiment where energy levels are observed directly, rather than transitions
NormPopDist - as for PopDist, but include partition function.

For the four with units (EinsteinA, nm2MHzperMolecule, nm2MHzperMolecule and HzperMolecule), transition moments are assumed to be in Debye for electric dipole transitions and Bohr or nuclear magnetons for magnetic dipole transitions.

Misleading results can be obtained for a setting of Arbitrary when simulating isotopologues or isotopomers with different symmetry or statistical weights together, such as ³⁵Cl₂ and ³⁵Cl³⁷Cl. The calculation is "correct", in that the partition function is necessary to give the correct relative intensities, but is excluded by design for this setting.

LifeModel

Model to use for state dependent lifetimes and linewidths. Valid values are lmNone, lmWidth, lmProduct, lmProductWidth, lmParent, lmParentWidth, lmGate, lmGateWidth. See Widths and Lifetime Effects for how this setting works.

PlotUnits

Units for the horizontal scale for spectrum plots. Possibilities are standard energy unit (cm1, MHz, Kelvin and eV) as in the Mixture object and also:

sqrtcm1 - Velocity in units of cm^-1/2
nmVac - Wavelength in vacuum in nm
nmAir - Wavelength in air in nm

nDF

Number of points (between Fmin and Fmax) to calculate the spectrum at. Note that if a peak width is less than 3*(Fmax-Fmin)/nDF, i.e. only a few points wide, then it is shown as a stick, rather than a peak.

WidthMult

Multiple of line width to extend convolution over.

ShowSum

Plot overall sum of individual spectra. This is toggled by the

button.

ShowParts

Plot individual spectra making up overall spectrum. The individual spectra are grouped by colour, so you will need to set colours to see something different to the sum. Colours can be set at the transition moment, state, molecule or species level. This is toggled by the

button.

ShowFortrat

Plot a Fortrat diagram, i.e. J against frequency, in the main window. This is toggled by the

button.

UseUpper

Set to use upper rather than lower state J and symmetry in the Fortrat diagram.

ShowSymmetry

Show symmetry in Fortrat plots.

ShowDeltaJ

Show change in J in Fortrat plots.

ScaleMarkSize

Scale Mark Size with intensity in Fortrat plots.

UseSymmetry

If true, show different symmetries in separate Fortrat plots.

UseStateNumber

If true, show different state numbers in separate Fortrat plots.

FortratQno

Select quantum number to use in Fortrat plots.

Parameters

Fmin

Left edge of plot range in main window.

Fmax

Right edge of plot range in main window.

Temperature

Rotational temperature (Kelvin).

Gaussian

Gaussian contribution to linewidth (full width half maximum). If both this and a Lorentzian width (below) is set the result is a convolution of the two, a Voigt profile.

Lorentzian

Lorentzian contribution to linewidth (full width half maximum). This and the Gaussian width can also be set from the main window.

Foffset

Frequency offset to simulation.

SMargin

Relative Size of peak to ignore when convoluting for contour fitting.

OThreshold

Ignore peaks smaller than this fraction of the maximum peak intensity.

RefWidth

Reference width in linewidth (predissociation) calculations; see LifeModel

Tvib

Vibrational Temperature (Kelvin); set to -1 (default) to use rotational temperature for all Boltzmann factors.

MinI

Set the scaling of mark sizes in Fortrat plots.

Saturation

Zero for normal calculation; positive values progressively switch strength to population only by replacing the line strength, S by:

S = (1-exp(-S*Saturation/g))*g

where g = Min(2J'+1, 2J"+1)*Statistical Weight. This is appropriate for saturation by z polarized light. Values of, say, 1 to 10 will wash out the differences between allowed branches and much higher values will bring out transitions that are only allowed by some weak mixing.

Tspin

Spin temperature (Kelvin); set to -1 (default) to assume equilibrated nuclear spin states. If set >=0 then the fraction of molecules with each particular nuclear spin species (ortho/para for diatomics) is fixed at the fractions found at T = Tspin. This is often appropriate for molecular beams, where the nuclear spin states do not relax during the expansion.

Note that the current implementation for asymmetric tops fails if the statistical weight for two different spin species is the same.

EField

Static electric field, V/m; see External Fields - The Zeeman and Stark Effects

BField

Static magnetic field in Tesla (= 10⁴ Gauss); see External Fields - The Zeeman and Stark Effects

Doppler

Plot each transition as two peaks, split by 2*Doppler*Centre Frequency. This gives the double peak structure often seen in Fourier transform microwave spectroscopy.

IntensityUnits	Units for intensity. These are described in detail under Intensity Formulae. Possible values are: Arbitrary - fastest, as it does not include the partition function, but can give misleading results (see below). Normalized - default, and recommended for most cases unless absolute intensities are required. Squared - square the calculated intensity HonlLondon - The line strength factors, essentially the transition dipole moment summed over all the degenerate M levels and squared. EinsteinASum - The Einstein A coefficient for each transition summed over upper and lower state M levels, with population factors excluded. This was EinsteinASum up to version 6.0.228. EinsteinA - The Einstein A coefficient for each transition summed over lower state M levels, with population factors excluded. This corresponds to the radiative rate from the upper state. nm2MHzperMolecule - for normal absorption cm2WavenumberperMolecule - for normal absorption HzperMolecule - for emission. This is the rate of emission of photons by one molecule on each transition, including the Boltzmann factor and partition function. PopDist - for a time of flight spectrum or similar experiment where energy levels are observed directly, rather than transitions NormPopDist - as for PopDist, but include partition function. For the four with units (EinsteinA, nm2MHzperMolecule, nm2MHzperMolecule and HzperMolecule), transition moments are assumed to be in Debye for electric dipole transitions and Bohr or nuclear magnetons for magnetic dipole transitions. Misleading results can be obtained for a setting of Arbitrary when simulating isotopologues or isotopomers with different symmetry or statistical weights together, such as ³⁵Cl₂ and ³⁵Cl³⁷Cl. The calculation is "correct", in that the partition function is necessary to give the correct relative intensities, but is excluded by design for this setting.
LifeModel	Model to use for state dependent lifetimes and linewidths. Valid values are lmNone, lmWidth, lmProduct, lmProductWidth, lmParent, lmParentWidth, lmGate, lmGateWidth. See Widths and Lifetime Effects for how this setting works.
PlotUnits	Units for the horizontal scale for spectrum plots. Possibilities are standard energy unit (cm1, MHz, Kelvin and eV) as in the Mixture object and also: sqrtcm1 - Velocity in units of cm^-1/2 nmVac - Wavelength in vacuum in nm nmAir - Wavelength in air in nm
nDF	Number of points (between Fmin and Fmax) to calculate the spectrum at. Note that if a peak width is less than 3*(Fmax-Fmin)/nDF, i.e. only a few points wide, then it is shown as a stick, rather than a peak.
WidthMult	Multiple of line width to extend convolution over.
ShowSum	Plot overall sum of individual spectra. This is toggled by the button.
ShowParts	Plot individual spectra making up overall spectrum. The individual spectra are grouped by colour, so you will need to set colours to see something different to the sum. Colours can be set at the transition moment, state, molecule or species level. This is toggled by the button.
ShowFortrat	Plot a Fortrat diagram, i.e. J against frequency, in the main window. This is toggled by the button.
UseUpper	Set to use upper rather than lower state J and symmetry in the Fortrat diagram.
ShowSymmetry	Show symmetry in Fortrat plots.
ShowDeltaJ	Show change in J in Fortrat plots.
ScaleMarkSize	Scale Mark Size with intensity in Fortrat plots.
UseSymmetry	If true, show different symmetries in separate Fortrat plots.
UseStateNumber	If true, show different state numbers in separate Fortrat plots.
FortratQno	Select quantum number to use in Fortrat plots.

Fmin	Left edge of plot range in main window.
Fmax	Right edge of plot range in main window.
Temperature	Rotational temperature (Kelvin).
Gaussian	Gaussian contribution to linewidth (full width half maximum). If both this and a Lorentzian width (below) is set the result is a convolution of the two, a Voigt profile.
Lorentzian	Lorentzian contribution to linewidth (full width half maximum). This and the Gaussian width can also be set from the main window.
Foffset	Frequency offset to simulation.
SMargin	Relative Size of peak to ignore when convoluting for contour fitting.
OThreshold	Ignore peaks smaller than this fraction of the maximum peak intensity.
RefWidth	Reference width in linewidth (predissociation) calculations; see LifeModel
Tvib	Vibrational Temperature (Kelvin); set to -1 (default) to use rotational temperature for all Boltzmann factors.
MinI	Set the scaling of mark sizes in Fortrat plots.
Saturation	Zero for normal calculation; positive values progressively switch strength to population only by replacing the line strength, S by: S = (1-exp(-SSaturation/g))g where g = Min(2J'+1, 2J"+1)*Statistical Weight. This is appropriate for saturation by z polarized light. Values of, say, 1 to 10 will wash out the differences between allowed branches and much higher values will bring out transitions that are only allowed by some weak mixing.
Tspin	Spin temperature (Kelvin); set to -1 (default) to assume equilibrated nuclear spin states. If set >=0 then the fraction of molecules with each particular nuclear spin species (ortho/para for diatomics) is fixed at the fractions found at T = Tspin. This is often appropriate for molecular beams, where the nuclear spin states do not relax during the expansion. Note that the current implementation for asymmetric tops fails if the statistical weight for two different spin species is the same.
EField	Static electric field, V/m; see External Fields - The Zeeman and Stark Effects
BField	Static magnetic field in Tesla (= 10⁴ Gauss); see External Fields - The Zeeman and Stark Effects
Doppler	Plot each transition as two peaks, split by 2DopplerCentre Frequency. This gives the double peak structure often seen in Fourier transform microwave spectroscopy.