Nuclear Hyperfine Structure in Asymmetric Tops

If the parent molecule has nNuclei non zero, then each state will have nNuclei of the items listed below (TAsymmetricTopNucleus). The following coupling scheme is normally used:
though an alternative scheme must be used for equivalent nuclei, as described under the AsNext setting.

Note that only nuclei not explicitly simulated with nucleus objects should be included in calculating the statistical weights (eeWt and so on). If all equivalent nuclei have been explicitly included, then the statistical weights should be calculated as if there were an additional pair of equivalent spin zero nuclei, which will mean some mean weighs will be zero. A simple check for correct operation is to compare the rotational structure with and without the nuclei explicitly included, with the weights calculated in the latter case including all nuclei. If the linewidth is set somewhat larger than the width of the hyperfine structure the spectra should appear identical.

For interactions between nuclei see Nuclear Spin - Nuclear Spin Coupling

Settings

Note that these two should be set at the molecule level, but are in fact implemented at the state level, with any change in these two properties copied to all the states in the molecule.

Spin	Nuclear spin. (Note that this setting should logically be at the molecule, rather than the state level. Changing a spin here will change the corresponding spins in any other states.)
AsNext	Set to indicate that this nucleus is equivalent to the following nucleus. This is required for molecules with a centre of symmetry, where nuclei not on the centre of symmetry must occur as equivalent pairs. In these circumstances all parameters are taken from the second of the two nuclei, and the modified coupling scheme: I12 = I1 + I2; F = J + I12 is used. This setting can also be used for molecules without low symmetry (C1, Ci, Cs), in which case the alternate coupling scheme is used but the nuclei are not forced to be identical. Note that equivalent nuclei are not currently implemented for D2 and D2h symmetry.
MaxDJ	Maximum ΔJ to include to consider in evaluating matrix elements for this nucleus. Default is negative, which includes all possible matrix elements, but setting this to zero (or possibly 1) can give significantly faster calculations but may be less accurate, particularly for low J.

Parameters

Note that where x, y and z axes are referred to below, the mapping to a, b and c axes is determined by the representation - see Symmetry and Axis Systems so that, for example, CHIzz corresponds to χ_aa in a Ir representation but χ_cc in a IIIr representation.

aF	Nuclear spin - electron spin Fermi Contact interaction (I.S).
Tzz	Tzz = -(Txx+Tyy) component of Nuclear spin - electron spin dipole dipole interaction.
Txxmyy	Txx-Tyy component of Nuclear spin - electron spin dipole dipole interaction.
Tab	ab component of Nuclear spin - electron spin dipole dipole interaction.
Tac	ac component of Nuclear spin - electron spin dipole dipole interaction.
Tbc	bc component of Nuclear spin - electron spin dipole dipole interaction.
CHIzz	zz component of Nuclear Quadrupole interaction.
CHIxxmyy	xx-yy component of Nuclear Quadrupole interaction.
CHIab	ab component of Nuclear Quadrupole interaction.
CHIac	ac component of Nuclear Quadrupole interaction.
CHIbc	bc component of Nuclear Quadrupole interaction.
Caa	aa component of Nuclear Spin - Rotation interaction.
Cbb	bb component of Nuclear Spin - Rotation interaction.
Ccc	cc component of Nuclear Spin - Rotation interaction.