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Custom Width Functions

Custom width functions provide an empirical way of specifying quantum number dependent line widths and intensities; see Widths and Lifetime Effects for the overall picture. These are created under the appropriate state object, and allow the width to be specified in terms of selected quantum numbers. A typical function might be:


which would be appropriate for an inhomogeneous predissociation, such as predissociation of a Σ state by a Π state. Use a negative width to indicate a state that should be excluded from the calculation, perhaps because it is above a dissociation limit.

Built In Variables

The width PGOPHER would use if Active is set to false
The state energy
J for the state
The symmetry number of the state
The eigenvalue number of the state
MJ for the state - only set if external fields are present
The origin of the vibronic state. This is normally the value of the Origin parameter for the state, but for linear molecules a correction is applied so that the value is approximately the  energy of the lowest rotational level. (A similar offset is applied in the vibrational structure mode.)
The AssumedOrigin for the molecule (if not set to the default) or else the lowest vibronic state origin (defined as above), considering only states for which Initial = True.
The calculated width for the state, before applying the custom width. This will be the same as the Result variable for this type of object.

Additional quantum numbers are also available, depending on the molecule type. They are based on the dominant basis state, so may not be exact for strongly mixed states.

For asymmetric tops the standard quantum numbers Ka and Kc are available.

For linear molecules:
The Omega quantum number
Fn The spin component, 1 for F1, 2 for F2, etc.
Note that for versions before 8.0.171 the values were divided by 2.

For symmetric tops:
The absolute value of K
Kl The sign of Kl but separably degenerate point groups have additional in this variable.

For vibrating molecules:
v1, v2, ...
Vibrational quantum numbers
l1, l2, ...
Vibrational angular momentum quantum number, for degenerate modes only.
Electronic orbital angular momentum, Λ.
Electronic angular momentum, Ω.

In addition any parameter can be referred to by giving the name in dotted notation. For example the current value of Tvib can be referred to using Simulation.Tvib.


Active Set true to use the function provided to calculate the width
nDebug If non zero, write the values of all the variables and the value of the function on each evaluation to the log window. See debugging for options on the output. To see any output the expression must not be blank - simply set to "Value" to see the defaults in action.