Energy relaxations in CS2 and in NO2–N2O4 vapors following pulsed laser excitation at 337.1 nm by probe beam deflection measurements

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Abstract
The pulsed photothermal generation and probe‐beam deflection technique was applied to monitor nonradiative relaxation and transport processes in CS2 and in NO2–N2O4 vapors following nitrogen laser excitation at 337.1 nm. A theoretical model is developed to describe the signal shape, and to derive the thermal diffusivity and energy relaxation time. The experiments were performed over a vapor pressure range of typically 1–100 Torr with a time resolution of 1 μs. In CS2 vapor of pressure above 10 Torr at room temperature, a slow heat release component is observed attributed to the photochemical formation of (CS)n particulates (‘‘laser‐snow’’). In NO2–N2O4 vapor, the experimental data provide the thermal diffusivity values in the pressure range of 1–100 Torr; these measurements support a ‘‘frozen equilibrium’’ model and indicate that any contribution due to the diffusional transport of chemical enthalpy for this system is small in this pressure range at room temperature. These experiments demonstrate that the photothermal probe‐beam deflection technique can provide useful information on heat‐release rates, for example, due to particulate formation, as well as measurement of thermal diffusivity, for example, in hostile and dissociative gas systems.

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