Helicity decoupling calculations

The body-fixed coupled equations are thus very similar in form to those for atom-diatom systems the only differences are that the potential matrix elements here are a generalisation of the atom-diatom case and that Hmon takes a more complicated form (and may have matrix elements off-diagonal in k). As for atom-diatom systems, considerable savings in computer time may be achieved by performing helicity decoupling calculations, in which the Coriolis matrix elements off-diagonal in K are neglected. 

Several decoupling approximations have been developed to simplify treatments where many rotational channels are coupled to begin with. A number of calculations have used orbital-rotational decoupling in the body-fixed frame, an il-dominant decoupling, and helicity decoupling. Several of these approaches have been recast in terms of effective Hamiltonians. Other decoupling treatments have extended the distorted-wave approximation by means of exponential operators or with optical potentials. 

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