Communication: Direct measurements of nascent O(³P_0,1,2) fine-structure distributions and branching ratios of correlated spin-orbit resolved product channels CO(ã³Π; v) + O(³P_0,1,2) and CO(Χ^~1Σ⁺; v) + O(³P_0,1,2) in VUV photodissociation of CO₂

We present a generally applicable experimental method for the direct measurement of nascent spin-orbit state distributions of atomic photofragments based on the detection of vacuum ultraviolet (VUV)-excited autoionizing-Rydberg (VUV-EAR) states. The incorporation of this VUV-EAR method in the application of the newly established VUV-VUV laser velocity-map-imaging-photoion (VMI-PI) apparatus has made possible the branching ratio measurement for correlated spin-orbit state resolved product channels, CO(ã³Π; v) + O(³P_0,1,2) and CO(Χ^~1Σ⁺; v) + O(³P_0,1,2), formed by VUV photoexcitation of CO₂ to the 4s(1₀¹) Rydberg state at 97,955.7 cm⁻¹. The total kinetic energy release (TKER) spectra obtained from the O⁺ VMI-PI images of O(³P_0,1,2) reveal the formation of correlated CO(ã³Π; v = 0–2) with well-resolved v = 0–2 vibrational bands. This observation shows that the dissociation of CO₂ to form the spin-allowed CO(ã³Π; v = 0–2) + O(³P_0,1,2) channel has no potential energy barrier. The TKER spectra for the spin-forbidden CO(Χ^~1Σ⁺; v) + O(³P_0,1,2) channel were found to exhibit broad profiles, indicative of the formation of a broad range of rovibrational states of CO(Χ^~1Σ⁺)  with significant vibrational populations for v = 18–26. While the VMI-PI images for the CO(ã³Π; v = 0–2) + O(³P_0,1,2) channel are anisotropic, indicating that the predissociation of CO₂ 4s(1₀¹) occurs via a near linear configuration in a time scale shorter than the rotational period, the angular distributions for the CO(Χ^~1Σ⁺; v) + O(³P_0,1,2) channel are close to isotropic, revealing a slower predissociation process, which possibly occurs on a triplet surface via an intersystem crossing mechanism