Role of Dispersion in Collision-Induced Absorption

It is shown that theoretical calculations which use the exponential model $\overrightarrow{\mu }={\mu }_0\left(\frac{\overrightarrow{\mathrm{r}}}{\mathcal{r}}\right)\times \exp (-\frac{\mathcal{r}}{\rho })$ for the variation of the dipole moment $\overrightarrow{\mu }$ with internuclear separation $\overrightarrow{\mathrm{r}}$ can be forced into agreement with experiment only if one uses dipole parameters ${\mu }_0$, $\rho$ which are in serious disagreement with values computed by the molecular Hartree-Fock approximation. On the basis of a Drude model calculation, it is concluded that the exponential model is an inadequate representation of the true physical situation because of its neglect of electron correlation effects.