A perspective view of the stagnation graph of the current density vector field of
methane CH 4 in a uniform external magnetic field B parallel to a C 2 symmetry axis
bisecting HCH angles (a system with D 2d ðS 4 Þ magnetic symmetry isomorphic to
D 2d ) shows branching points occurring at a short distance (%Æ0:4 bohr) from the C
nucleus, see Fig. 9 of Ref. [102]. An analogous representation of the SG of J
B of a
distorted ethane molecule C 2 H 6 , in the presence of uniform external magnetic field
parallel to the C–C bond axis, with magnetic symmetry D 3 ðC 3 Þ, contains eight (3,
±1) foci along the threefold symmetry axis, which indicates that the diatropic
electron flow spirals about it and that closed current density loops are absent. This is
confirmed by the corresponding streamline map, showing a single diatropic trajectory spiralling about the C 3 symmetry axis [102]. This pattern can be compared
Fig. 7.15 Perspective view of the current density vector field in ethane C 2 H 6 , with magnetic
symmetry D 3h ðC 3h Þ. The uniform external magnetic field B is parallel to the C–C bond axis
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P. Lazzeretti