State-to-state photodissociation dynamics of CO2 at 157 nm

Abstract

State-to-state photodissociation of CO₂(v₂ = 0 and 1) at 157 nm via the O(¹D) + CO(X¹Σ⁺) channel was studied by using the sliced velocity map imaging technique. Both the O(¹D) and CO(X¹Σ⁺) products were detected by (2 + 1) resonance enhanced multiphoton ionization (REMPI). Detection of CO via the B¹Σ⁺ ←← X¹Σ⁺ transition allowed ro-vibrational state-selective detection, and combined with imaging, the fragment energy and angular distributions have been derived. For CO(v = 0 and 1|j) products from the CO₂(v₂ = 0) molecule, the angular distributions of low-j CO display positive anisotropic parameters (about 0.8); with j increasing, the product anisotropic parameters gradually reduce to zero. While for CO(v = 0 and 1|j) products from the vibrational excited CO₂(v₂ = 1) molecule, the angular distributions of low-j CO also display positive anisotropic parameters; with j increasing, the product anisotropic parameters first decrease to zero and then become negative (about −0.5). Experimental results show that the observed variation of the product angular distribution with the rotational quantum number of CO is consistent with trends predicted by a classical model for non-axial fragment recoil. The results support advanced theoretical predictions of a predominantly parallel transition to the bent 2¹A′ excited state of CO₂, where bending introduces torque during the direct dissociation process.