The photothermal probe beam deflection method was applied to monitor photochemical particulation induced by a pulsed N2 laser in a CS2 vapor. The signal indicates a fast heat release due to collisional relaxation of excited CS2, and a slow heat release that can be ascribed to the aggregation of carbon monosulfide. The measured signal was modelled by solving the heat conduction equation for the geometry employed. This yields a value for the nucleation and growth time in the microsecond range when literature values for the collisional deactivation and the thermal diffusivity of CS2 are used. © 1985.