Molecular Quadrupoles and Atomic Shielding Factors

The electronic quadrupole moments of ${\mathrm{H}}_2^{+}$ and ${\mathrm{H}}_2$ are quadratic in the internuclear distance $R$ at short distances and the coefficient of proportionality is the quadrupole shielding factor of the ${\mathrm{He}}^{+}$ or He atom, respectively. The behavior of the quadrupole moment of ${\mathrm{H}}_2^{+}$ at short and long distances can be used to approximate it at all distances.