The existence of BH3 in the gas phase has been established
even though the molecule readily dimerizes; the bonding in
B2H6 is described in Section 4.7. The BH3 molecule belongs
to the D3h point group. By considering the orbital interactions
between the atomic orbitals of the B atom and the
LGOs of an appropriate H3 fragment, we can establish a
molecular bonding scheme. We begin by choosing an
appropriate axis set; the z axis coincides with the C3 axis of
BH3 and all of the atoms lie in the xy plane. Part of the
D3h character table is shown in Table 4.1. By using the
same approach as we did for the orbitals of the O atom in
H2O, we can assign symmetry labels to the orbitals of the
B atom in BH3: