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 CO(A 1Π) by photodissociation of CO2 from threshold to 635 Å· Above 685 Å the CO(A 1Π) cross section is of the order 1 × 10−12 cm2 and exhibits considerable structure while below 685 Å the CO(A 1Π) cross section rapidly drops to a nearly constant value of [sine wave] 3 × 10−20 cm2. 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 CO(A 1Π) cross section was inferred for producing O(3S). Although not directly observed, evidence was obtained that the production of CO(A 1Π) is accompanied by production of O(1D) and O(1S) at incident photon wavelengths less than 800 and 700 Å, respectively. The CO(A 1Π−X1Σ) 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.