Abstract: | Pyrolytic decay of carbon diselenide was monitored by ultraviolet absorption spectroscopy in reflected shock waves in the temperature range of 1600–2600°K. The temperature dependence of the absorption coefficient of CSe2 at 2308 Å was determined and was used to provide kinetic information along with a deconvolution procedure which accounted for and removed systematic distortions of the fast time-resolved absorbance profile. For temperatures of 1600–2600°K and argon densities of 1.5–7.0 × 10?5 mol/cm3 dilute (1.0–9.0 × 10?9 mol/cm3) CSe2 pyrolyzed with measured first-order decay rates in the range of log10 k1 (sec?1) = 3.0?5.7; at midrange (2100°K and 4.3 × 10?5 mol/cm3 in Ar) k1 ≈ 3 × 104 sec?1. The decay probably occurs via a unimolecular low-pressure process, first order in both CSe2 and Ar, for which k2 ± 109 cm3/mol·sec at 2100°K. The deconvoluted data yield Arrhenius activation energies of 53.2 kcal/mol under second-order treatment, but the activation energy is less reliable than the general magnitude of the rate constant. A comparison of CSe2 with other molecules which are isoelectronic in their valence shells (CO2, CS2, OCS, and N2O) is made. |