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Ohio State University

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Absorption bands have been found in the ultraviolet spectra of solutions of iodine in a number of ``inert'' solvents such as saturated hydrocarbons and alkyl halides which are not found in the spectra of either iodine or the solvents alone. These bands are attributed to molecular complexes between iodine and the solvents such as have been previously reported for solutions of iodine in aromatic and olefinic hydrocarbons. It is shown that a relationship exists between the frequencies of the absorption bands of all the iodine complexes and the ionization potentials of the corresponding bases (solvents). This work has led to a simple extension of Mulliken's theory of molecular $complexes^{1}$ to the prediction of the frequencies of the absorption bands of the complexes. It is shown that \begin{equation}h\nu=(I_{B} - E_{A} - \frac{e^{2}}{r} + C_{AB}) {[1 + \left(\frac{b}{a}\right)^{2} + \left(\frac{b^{\ast}}{a^{\ast}}\right)^{2}]}\end{equation} where $h_{\nu}$ is the absorption frequency of the iodine complex $I_{B}$ is the ionization potential of the base $E_{A}$ is the electron affinity of the acid $e^{2}/r$ is a coulomb attraction term $C_{AB}$ is the sum of all other energy terms and $a, b, a^{\ast}$ and $b^{\ast}$ are normalization coefficient of the ground and excited state wave functions. A discussion is given of the observed frequency - ionization- potential relationship in the light of equation (1) above, taking into account the fact that the equation applies to the gas phase whereas the experiments were carried out in solution. The effects of variations in $C_{AB}$, r, and the normalization coefficients are also discussed.


Author Institution: Humble Oil and Refining Company; Departments of Physics and Chemistry, The University of Texas