Preparation of cationic intermediates by dissociative photoionization of van der Waals complexes. C₆H₆Cl⁺ from a C₆H₆ + HCl mixture

The ion [C₆H₆Cl]⁺ (1) has been observed as a product of dissociative photoionization of a C₆H₆ + HCl van der Waals complex. It was shown that 1 does not come from the dimer C₆H₆·HCl but from trimers or larger clusters, most likely (C₆H₆)₂HCl. Experiments with C₆D₆ + HCl mixtures demonstrate that the departing hydrogen initially belonged to the HCl partner of the complex. The energetics and isotope studies are consistent with an ipso structure for C₆H₆Cl⁺, i.e., a Wheland σ-complex. The overall process of dissociative photoionization does not have an accessible reaction channel leading to C₆H₆Cl⁺ unless at least one "solvent" molecule is present. Mechanisms by which the transformation may occur are discussed.