On the Formation of S(³ P) and S(¹ D) During the Thermal Decomposition of COS Behind Shock Waves

Abstract

The formation of ground state S(³ P) and electronically excited S(¹ D) atoms was studied during the thermal decomposition of carbonyl sulfide behind reflected shock waves by using atomic resonance absorption spectroscopy (ARAS). The experiments were performed in highly diluted mixtures of Ar with relative concentrations of COS between 4 to 100 ppm in the temperature range 1830 K ≤ T ≤ 3020 K at pressures around 1 bar. The measured slopes of the linear S(³ P) and S(¹ D) concentrations divided by the respective concentration of the initial reactants were found to obey the Arrhenius laws:

$$\frac{{d[S{(^3}P)]/dt}}{{[COS][Ar]}}{|_{t \approx 0}} = 2.9 \times {10^{14}} \times \exp (\frac{{63360cal/mol}}{{RT}})c{m^3}mo{l^{ - 1}}{s^{ - 1}}$$

((1))

$$\frac{{d[S{(^1}D)]/dt}}{{[COS][Ar]}}{|_{t \approx 0}} = 4.8 \times {10^{12}} \times \exp (\frac{{71800cal/mol}}{{RT}})c{m^3}mo{l^{ - 1}}{s^{ - 1}}$$

((2))

These results indicate a fast thermalisation of the partial equilibrium between the S³ P) and S(¹ D) states during the non-equilibrium dissociation of COS.