Perturbations describe an
interaction between two states. To add a perturbation, right-click
on the manifold in which the perturbation is required, and select
"Add new..."). The state(s) involved must also be specified; right
click on the perturbation and select Rename to bring up a dialog box to select the
states involved. There can be several perturbations acting between
any pair of states if required. It can also be useful to have a
perturbation acting within a particular state, as this can be used
to add terms to the Hamiltonian that are not part of the standard
Hamiltonian for the molecule, such as higher powers of J in centrifugal distortion.
These settings are common to all
perturbations; more specific settings are included in the sections
see the actual matrix elements used in any particular case, right
click on the perturbation and select "Matrix Elements". The
resulting expressions will be displayed in the log window, and
should be understood as being multiplied by the Value
||Index, starting from 1, of nuclear spin involved in
perturbation; 0 (default) for normal case where the
perturbation does not involve a nuclear spin.
||Scale factor with respect to preceding perturbation
||Size of perturbation. This is a simple numerical
multiplier of the matrix elements.