Picosecond Time Resolved Absorption Experiments of Iodine in Complexing Solvents

Abstract

Transient absorption spectra of I2 diluted in “inert” (CCl4, n-heptane) solvents and electron donor solvents of increasing complexing strength (CS2, benzene, dioxane, pyridine) have been measured (in the spectral range 400–800 nm) at different times (from 20 ps to 1 ns) after excitation using 25 ps pulses at λ = 532 nm. In inert solvents, the time evolution of the transient spectra are consistent with the model recently proposed by Harris et al.1Such a behaviour is in marked contrast with the experimental observation in strongly complexing solvents (pyridine). This is interpreted as resulting from a competition between geminate recombination and formation of a complex between the solvent and atomic iodine (I•) formed by the photodissociation process. In intermediate complexing solvents these two processes seem to coexist.