of the Td character table. The C3 axes in CH4 coincide
with the CH bonds, and the C2 and S4 axes coincide with
the x, y and z axes defined in Figure 4.6. Under Td symmetry,
the orbitals of the C atom in CH4 (Figure 4.20a) are classified
as follows:
. the 2s orbital has a1 symmetry;
. the 2px, 2py and 2pz orbitals are degenerate and the
orbital set has t2 symmetry.
In order to construct the LGOs of the H4 fragment in
CH4, we begin by working out the number of H 1s orbitals
left unchanged by each symmetry operation of the Td point
group. The result is summarized in the row of characters: