  Experimental, theoretical, and additive-model photoabsorption cross-sections
combined with constraints provided by the Kuhn-Reiche-Thomas sum rule and the
high-energy behavior of the dipole-oscillator-strength density are used to
construct dipole oscillator strength distributions for benzene, pyridazine
(1,2-diazine), pyrimidine (1,3-diazine), pyrazine (1,4-diazine), $s$-triazine
(1,3,5-triazine), toluene (methylbenzene), hexafluorobenzene, and nitrobenzene.
The distributions are used to predict dipole sum rules $S(k)$ for $-6 \le k \le
2$, mean excitation energies $I(k)$ for $-2 \le k \le 2$, and isotropic van der
Waals $C_{6}$ coefficients. A popular combination rule for estimating $C_{6}$
coefficients for unlike interactions from the $C_{6}$ coefficients of the like
interactions is found to be accurate to better than 1\% for 606 of 628 cases
(96.4\%) in the test set.
