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Coulostatic‐flash irradiation of semiconductor/liquid‐junction cells with a pulsed laser source has allowed time‐resolved measurements of photopotential transients in the submicrosecond time domain. In 1.0M electrolyte ∼12 nsec rise times were observed with several different normaln‐TiO2 electrodes. The dependences of transient photopotentials on the initial potential, pulsed laser intensity, and nature of electrolyte have been studied, and the measurement limitations defined by experimental and instrumental parameters have been described. Most importantly, the time dependence of photopotential transients has been characterized. Four possible contributions to the transient behavior are discussed: electron‐hole recombination, photoinduced charge transfer at the solution interface (oxidation), subsequent back‐reaction of photoproducts (reduction), and a transient expansion of the space charge layer due to rapid photoinduced charge injection.

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Laser-induced molecular fluorescence Is shown to be a sensitive and selective means for determining representative polycyclic aromatic hydrocarbons (PAH) In aqueous solutions. The limits of detection of benzene, naphthalene, anthracene, fluoranthene, and pyrene were found to be 19 ppb, 1.3 ppt (parts-per-trlllion), <4.4 ppt, 1.0 ppt, and 0.5 ppt, respectively. All the PAH fluorescence exhibits a linear dependence on concentration, sometimes extending over six orders In magnitude. Improvements In second harmonic generation and UV lasers should result In even lower minimum detectabilities, especially for anthracene.