Cross sections for production of the CO(A 1Π−X 1Σ) Fourth Positive band system and O(3S) by photodissociation of CO2

Excitation cross sections were measured for producing $\mathrm{CO}{\mathrm{(A\hspace{0.17em}}}^1\mathrm{\Pi )}$ by photodissociation of CO₂ from threshold to 635 Å· Above 685 Å the $\mathrm{CO}{\mathrm{(A\hspace{0.17em}}}^1\mathrm{\Pi )}$ cross section is of the order ${\text{1 × 10}}^{\text{−12}}\hspace{0.17em}{\mathrm{cm}}^2$ and exhibits considerable structure while below 685 Å the $\mathrm{CO}{\mathrm{(A\hspace{0.17em}}}^1\mathrm{\Pi )}$ cross section rapidly drops to a nearly constant value of ${\text{[sine wave] 3 × 10}}^{\text{−20}}\hspace{0.17em}{\mathrm{cm}}^2$ . The structure below 790 Å correlates with predissociation from known Rydberg states of CO₂ demonstrating the competition between preionization and predissociation. An upper limit of 6% of the $\mathrm{CO}{\mathrm{(A\hspace{0.17em}}}^1\mathrm{\Pi )}$ cross section was inferred for producing O(³S). Although not directly observed, evidence was obtained that the production of $\mathrm{CO}{\mathrm{(A\hspace{0.17em}}}^1\mathrm{\Pi )}$ is accompanied by production of O(¹D) and O(¹S) at incident photon wavelengths less than 800 and 700 Å, respectively. The $\mathrm{CO}{\mathrm{(A\hspace{0.17em}}}^1{\mathrm{\Pi -X}}^1\mathrm{\Sigma )}$ vibrational intensity distribution was obtained with 7 Å resolution for 16.69 eV photon impact and is similar to a 20 eV electron impact produced distribution.