Dipole oscillator strength distributions, sum rules, mean excitation energies, and isotropic van der Waals coefficients for benzene, pyridazine, pyrimidine, pyrazine, s-triazine, toluene, hexafluorobenzene, and nitrobenzene

Abstract

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.