Shock-Tube Study of Carbon Monoxide Dissociation Using Vacuum-Ultraviolet Absorption

The dissociation kinetics of carbon monoxide diluted in argon and in mixtures of oxygen in argon have been investigated over the temperature range 8000–15 000°K behind reflected shocks using light absorption at 1176 Å. An induction period, 5–100 times longer than the vibrational relaxation time of carbon monoxide, was observed in the carbon monoxide–argon mixtures prior to the establishment of the steady‐state dissociation rate for the over‐all process, $$\mathrm{CO}+\mathrm{M}\to {\displaystyle {lim}^{k_d^{\mathrm{(M)}}}}\mathrm{C}+\mathrm{O}+\mathrm{M}.$$ Rate coefficients were determined for Ar, CO, and O as the collision partner, M. The steady‐state dissociation rate coefficient, $k_d^{\mathrm{(Ar)}}$ , was found to be well represented by the expression $k_d^{\mathrm{(Ar)}}{\text{\hspace{0.17em}=\hspace{0.17em}2.8\hspace{0.17em}×\hspace{0.17em}10}}^{\text{3\hspace{0.17em}±\hspace{0.17em}0.08}}{T}^{\text{−2.86\hspace{0.17em}±\hspace{0.17em}0.14}}\mathrm{\hspace{0.17em}\times \hspace{0.17em}}\exp {\text{\hspace{0.17em}−\hspace{0.17em}(1.29\hspace{0.17em}×\hspace{0.17em}10}}^5\mathrm{\hspace{0.17em}/\hspace{0.17em}T)}{\mathrm{cm}}^3{\sec }^{\text{−1}}$ , with $k_d^{\mathrm{(CO)}}{\text{\hspace{0.17em}≲\hspace{0.17em}2k}}_d^{\mathrm{(Ar)}}$ and $k_d^{\mathrm{(O)}}{\text{\hspace{0.17em}=\hspace{0.17em}15 k}}_d^{\mathrm{(Ar)}}$ . Induction time measurements reported here are in excellent agreement with the previous measurements of Fairbairn and in reasonable accord with the transient behavior of mechanisms in which either of the following reactions: CO + C(or O)→CO* + C(or O) or CO + C→C₂ + O, may be involved in the transient buildup of the steady‐state intermediates CO* or C₂. The measured induction times, $\tau$ , of this and the previous studies are best correlated by the relationship ${\mathrm{[\tau }}^2(\mathrm{CO}\mathrm{)(}\mathrm{M}{\mathrm{)]}}^{\text{−1}}{\text{\hspace{0.17em}=\hspace{0.17em}4.97\hspace{0.17em}×\hspace{0.17em}10}}^{\text{−19\hspace{0.17em}±\hspace{0.17em}0.18}}\exp \text{\hspace{0.17em}−\hspace{0.17em}[(132 400\hspace{0.17em}±\hspace{0.17em}3300)\hspace{0.17em}/\hspace{0.17em}T]}{\mathrm{cm}}^6{\sec }^{\text{−2}}$ . Mechanisms are advanced to account for the measured induction behavior and steady‐state dissociation rates.