Diffusion of electrically neutral radicals and anion radicals created by photochemical reactions

Diffusion processes of the intermediate radicals created by the photochemical reactions of ketones in alcoholic solvents are investigated by using the transient grating (TG) method. The electrically neutral radicals and the anion radicals of acetophenone, benzaldehyde, xanthone, benzophenone and benzil were created selectively by controlling the concentration of sodium hydroxide (NaOH) in alcoholic solvents. The translational diffusion constants (D) of the anion radicals, the neutral radicals, and the parent stable molecules can be successfully measured under the same conditions by this method. It is found that both the neutral and anion radicals diffuse slower than the parent molecules. Values of D of the anion radicals, the neutral radicals and the parent molecules are compared in detail in wide ranges of solvent viscosities, solute sizes and temperatures. Under any conditions, D values of the charged radicals are similar to those of the neutral radicals. A possible origin of such a similarity is discussed in term of the intermolecular charge polarizabilities of the radicals.