Spectral investigation of molecular ionization on the surface of alumosilicates

Abstract The adsorption of the oxidizable aromatic amines (dipbenylamine, benzidine, dimethyl p -phenylene diamine) from the gas phase in vacuo on the surface of alumosilica gels, produces an absorption spectrum and a EPR signal of the positive molecular ion-radical. In the absorption spectrum of the aromatic polynuclear hydrocarbons (naphthalene, anthracene, perylene, tetracene) two kinds of visible bands appear upon adsorption of their vapours in vacuo on Al 2 O 3 -SiO 2 gels. The one belongs to the positive molecular ion radical and is accompanied by a EPR signal, the other is produced by the addition of a proton to the hydrocarbon (carbonium ion). The two types of active sites present on the surface can be discriminated by ionic exchange of the protons for alkali cations. No such spectral effects are observed for silica and alumina gels separately, but could be found for other adsorbents.