Résumé : The interaction between 1‐chloronaphthalene and dimethylmercury in their electronic ground state has been examined by visible absorption spectroscopy. In the presence of the organometallic molecule, the first singlet to triplet absorption band of 1‐chloronaphthalene is strongly enhanced. The variations of the optical density at 427.5 nm are used to determine the stoichiometry and the concentration of a possible ground state complex between the two species as a function of the mole fraction of dimethylmercury. From the consideration of the experimental thermodynamic parameters for the assumed equilibrium: (Formula Presented.) it appears that there is no strong case for such a complex. These results strengthen our previous interpretation of aromatics' fluorescence quenching by dimethylmercury. Copyright © 1973 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim