The CO2 Photolysis Problem

Abstract

The photolysis of CO2 has been investigated at 1470 Å to determine the O(1D) quantum yield and the subsequent O(3P) yield resulting from O(1D) deactivation, the O(1D)–CO2 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, O(3P) 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 O(3P) atom. This observation suggests that all previous determinations of low O2/CO ratios in CO2 photolysis relate to effects taking place after O(3P) has been produced, and it is quite likely that wall absorption of O(3P) is the dominant process. By utilizing competitive quenching between CO2, H2, and N2, it was determined that the O(1D) quantum yield is unity, and that the rate constant ratio for O(1D) deactivation by N2 and CO2, kN2 / kCO2, 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.