The wave equation for the photoacoustic effect generated by heat deposition and molecular volume change is solved for a one-dimensional geometry for the case of excitation of a single molecular electronic state that decays to the ground state exponentially in time. The solution for a uniformly illuminated, infinite layer of fluid in contact with two infinite fluid or solid half-spaces, corresponding to a recently developed experimental geometry for generation of the photoacoustic effect is given, The solutions show the effects of finite decay of the excited state and of reflections at the interfaces.