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.