Study on the [1+1′] photodissociation spectra of CO2+ via C2Σg+←B2Σu+/A2Πu,1/2←X2Πg,1/2 transitions

Dissociation dynamics of carbon dioxide cation (CO2 +) in the C2Σg + state via [1+1] two-photon excitation

The dissociation dynamics of CO₂ ⁺ in the C²Σ_g ⁺ state has been studied in the 8.14-8.68 eV region by [1+1] two-photon excitation via vibronically selected intermediate A²Π_u and B²Σ_u ⁺ states using a cryogenic ion trap velocity map imaging spectrometer. The cryogenic ion trap produces an internally cold mass selected ion sample of CO₂ ⁺. Total translational energy release (TER) and two-dimensional recoiling velocity distributions of fragmented CO⁺ ions are measured by time-sliced velocity map imaging. High resolution TER spectra allow us to identify and assign three dissociation channels of CO₂ ⁺ (C²Σ_g ⁺) in the studied energy region: (1) production of CO⁺(X²Σ⁺) + O(³P) by predissociation via spin-orbit coupling with the repulsive 1⁴Π_u state; (2) production of CO⁺(X²Σ⁺) + O(¹D) by predissociation via bending and/or anti-symmetric stretching mediated conical intersection crossing with A²Π_u or B²Σ_u ⁺, where the C²Σ_g ⁺/A²Π_u crossing is considered to be more likely; (3) direct dissociation to CO⁺(A²Π) + O(³P) on the C²Σ_g ⁺ state surface, which exhibits a competitive intensity above its dissociation limit (8.20 eV). For the first dissociation channel, the fragmented CO⁺(X²Σ⁺) ions are found to have widely spread populations of both rotational and vibrational levels, indicating that bending of the parent CO₂ ⁺ over a broad range is involved upon dissociation, while for the latter two channels, the produced CO⁺(X²Σ⁺) and CO⁺(A²Π) ions have relatively narrow rotational populations. The anisotropy parameters β are also measured for all three channels and are found to be nearly independent of the vibronically selected intermediate states, likely due to complicated intramolecular interactions in the studied energy region.