Figure 2.

Symmetry properties of the lowest non-zero spherical multipole moments of water molecule. Shown are the corresponding charge distributions. From left to right: coordinate system; a dipole, p; a linear quadrupole, Q₀; a square quadrupole, Q₂; a linear octupole, Ω₀, and a cubic octupole, Ω₂. These moments are related to the Cartesian components of the traceless multipole moments of water molecule as Q₀ = Q_zz, Q₂ = 1/2 (Q_yy − Q_xx), Ω₀ = Ω_zzz, Ω₂ = 1/2 (Ω_yyz − Ω_xxz).³¹