Effects of exothermic chemical reaction on the photoacoustic effect from particulate suspensions

Irradiation of chemically reactive particulate suspensions by high power, pulsed laser radiation initiates reactions at the sites of the particles so that besides the absorbed optical energy, chemical energy is liberated. In addition to the release of chemical energy, chemical reaction can result in gas production both of which result in enhancement in the amplitude of the photoacoustic effect. Here we report photoacoustic and transient grating experiments with colloidal C in mixtures of H(2)O(2) with H(2)O. The inclusion of H(2)O(2) in an aqueous C suspension changes the normally endothermic reaction of C with H(2)O into the highly exothermic reaction of C with H(2)O(2) leading to both an enhanced photoacoustic effect and an increase in light emission from the suspension. As well, laser-initiated exothermic reactions in suspensions of C with CH(3)NO(2) and particulate Hg(CNO)(2) in H(2)O are shown to result in greatly enhanced photoacoustic signal amplitudes.