Pyrolytic production of Se ( 3 P ) from carbon diselenide. II. Rate of CSe 2 decay

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 CSe 2 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/cm 3 dilute (1.0–9.0 × 10 −9 mol/cm 3 ) CSe 2 pyrolyzed with measured first‐order decay rates in the range of log 10 k 1 (sec −1 ) = 3.0−5.7; at midrange (2100°K and 4.3 × 10 −5 mol/cm 3 in Ar) k 1 ≈ 3 × 10 4 sec −1 . The decay probably occurs via a unimolecular low‐pressure process, first order in both CSe 2 and Ar, for which k 2 ± 10 9 cm 3 /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 CSe 2 with other molecules which are isoelectronic in their valence shells (CO 2 , CS 2 , OCS, and N 2 O) is made.