State-to-state photodissociation dynamics of CO2 around 108 nm: the O(1S) atom channel

Abstract

State-to-state photodissociation of carbon dioxide (CO₂) via the 3p¹Π_u Rydberg state was investigated by the time-sliced velocity map ion imaging technique (TSVMI) using a tunable vacuum ultraviolet free electron laser (VUV FEL) source. Raw images of the O(¹S) products resulting from the O(¹S) + CO(X¹Σ⁺) channel were acquired at the photolysis wavelengths between 107.37 and 108.84 nm. From the vibrational resolved O(¹S) images, the product total kinetic energy releases and the vibrational state distributions of the CO(X¹Σ⁺) co-products were obtained, respectively. It is found that vibrationally excited CO co-products populate at as high as v = 6 or 7 while peaking at v = 1 and v = 4, and most of the individual vibrational peaks present a bimodal rotational structure. Furthermore, the angular distributions at all studied photolysis wavelengths have also been determined. The associated vibrational-state specific anisotropy parameters (β) exhibit a photolysis wavelength-dependent feature, in which the β-values observed at 108.01 nm and 108.27 nm are more positive than those at 107.37 nm and 107.52 nm, while the β-values have almost isotropic behaviour at 108.84 nm. These experimental results indicate that the initially prepared CO₂ molecules around 108 nm should decay to the 4¹A′ state via non-adiabatic coupling, and dissociate in the 4¹A′ state to produce O(¹S) + CO(X¹Σ⁺) products with different dissociation time scales.