The CO2 Photolysis Problem

Abstract

The photolysis of CO₂ has been investigated at 1470 Å to determine the $\mathrm{O}{(}^1\mathrm{D)}$ quantum yield and the subsequent $\mathrm{O}{(}^3\mathrm{P)}$ yield resulting from $\mathrm{O}{(}^1\mathrm{D)}$ deactivation, the $\mathrm{O}{(}^1\mathrm{D)–}{\mathrm{CO}}_2$ interaction rate constant, and the possible role of CO₃ in the over‐all process. Utilizing the 1302–1306‐Å Oi triplet as a resonance fluorescence source, ${\mathrm{O(}}^3\mathrm{P)}$ atoms were monitored during O₂ and CO₂ photolysis. By measuring both the intensity and decay time constants for the fluorescence, it could be concluded that each photon absorbed by CO₂ ultimately resulted in an $\mathrm{O}{(}^3\mathrm{P)}$ atom. This observation suggests that all previous determinations of low O₂/CO ratios in CO₂ photolysis relate to effects taking place after $\mathrm{O}{(}^3\mathrm{P)}$ has been produced, and it is quite likely that wall absorption of $\mathrm{O}{(}^3\mathrm{P)}$ is the dominant process. By utilizing competitive quenching between CO₂, H₂, and N₂, it was determined that the $\mathrm{O}{(}^1\mathrm{D)}$ quantum yield is unity, and that the rate constant ratio for $\mathrm{O}{(}^1\mathrm{D)}$ deactivation by N₂ and CO₂, $k_{N_2}{\mathrm{\hspace{0.17em}/\hspace{0.17em}k}}_{{\mathrm{CO}}_2}$ , is 0.26, in excellent agreement with other investigations, giving a CO₂ rate constant of 3 ± 1 × 10⁻¹⁰ cm³ molecule⁻¹·sec⁻¹. Attempts to find effects attributable to CO₃ participation in the system were unsuccessful, and the implications for planetary atmosphere models are discussed.