Measurement of O($^1$D) formation during thermal decomposition of CO$_2$ behind shock waves

Abstract.

Atomic Resonance Absorption Spectroscopy (ARAS) was applied to measure the time dependent concentration of electronically excited O($^1$D)-atoms during the thermal decomposition of CO$_2$ behind reflected shock waves. The experiments were performed in the temperature range 4102 K $\le$ T $\le$ 6375 K at pressures 0.2 to 1.9 bar with initial gas mixtures of 100 to 1000 ppm CO$_2$ diluted in Ar. The measured O($^1$D)-formation rate at early reaction times divided by the initial reactant concentrations was found to obey the Arrhenius law: \beo &&\frac{d[{\rm O(^1D)}]/dt}{{\rm [CO_2]_0 \, [Ar]}} \Biggr|_{t \approx 0} \\ &&\quad = 1.23 \times 10^{14} \exp \left( -74810 {\rm K}/T \right){\rm cm^{3} mol^{-1} s^{-1}} \eeo The assumption of a fast thermalisation between the O($^3$P) and O($^1$D) states is in agreement with previous measurements of the O($^3$P) formation during the thermal decomposition of CO$_2$, see Burmeister and Roth (1990).