A study on the excited states of liquid p-dioxane by means of picosecond pulse radiolysis

Abstract

The flourescence phenomena in liquid p-dioxane systems were investigated by pulse radiolysis technique, and at the same time, comparative 200 nm steady-state photoexcitation experiments were carried out. The spectra ontained by the two excitation methods are in good agreement with each other. This indicates that the same fluorescent excited states are formed. The pulse radiolysis of neat p-dioxane showed that the fluorescence has a clear growth in 1 ns after irradiation and its time profile is independent of wavelength. The formation of the state could be explained well by geminate ion recombination of holes and electrons. The lifetime and G-value of the state were determined to be 2.6 ± 0.2 ns and 1.0 ± 0.1 at 18°C, respectively. In the presence of a polar solute, such as water or alcohol, the emission spectrum is shifted to a longer wavelength region. It has been found that the growth of emission is dependent on wavelength, while the lifetime is independent. On the other hand, addition of a non-polar solute, such as isooctane or cyclohexane, makes a slight shift of the emission spectrum to a shorter wavelength region and the decay becomes faster. For all systems, the yields of emission and the lifetimes for the excited states were measured as a function of concentration of additives. Furthermore, measurements were made for ternary mixture systems ( p-dioxane, water and isooctane or cyclohexane). Based on the above experimental results, the excitation process in the liquid p-dioxane systems is discussed.