There will be one of these for each perturbation parameter in each
state.
Settings
Nucleus
Index, starting from 1, of the nuclear spin involved in
perturbation; 0 (default) for those not involving a nuclear spin.
Op
Perturbation type. This can be LS, Luncouple, Homog,
aL, e or eQq1, where LS is the spin-orbit perturbation, Luncouple is
the L-uncoupling perturbation, LJS is the J-dependent version of LS,
and aL, e and eQq1 are hyperfine perturbations.
n
Power of operator in perturbation - not currently used.