Solute-Induced Photo-Ionization of Nonpolar Liquids

Transient dc conductivity measurements of anthracene solutions in cyclohexane have provided evidence for solvent ionization following irradiation with 248 nm excimer laser pulses. A mechanism resulting in a cyclohexane cation and an anthracene anion as near neighbors can explain the experimental observations: a high mobility species, 7 to 8 absorbed photons per solute molecule, intensity dependence, and absence of enhanced hydrogen generation. The nature of the high-mobility species is discussed and the contribution of geminate ions to transient dc conductivity measurements is analyzed. A photo-ionization apparatus with 20 ps time resolution is being developed to observe the transient ions spectroscopically. Such a system may enable observation of solute-induced ionization in solvents having normal mobility cations.