Perturbations

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 for linear, symmetric, asymmetric and vibrating molecules. To 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 parameter.