Cross section measurements for photodetachment or photodissociation of ions produced in gaseous mixtures of O2, CO2, and H2O

Photodissociation Dynamics of the [O2-H2O]+ Ionic Complex

We present an experimental study on the photodissociation dynamics of [O₂-H₂O]⁺ in the 580-266 nm wavelength range using a cryogenic ion trap velocity map imaging spectrometer. The cryogenic ion trap produces mass selected and internally cold [O2-H2O]+ ions for photodissociation. By detecting both the O₂⁺ and H₂O⁺ photofragments using the time-of-flight mass spectrometry and velocity map imaging techniques, branching ratios and total kinetic energy release distributions of the O₂⁺ + H₂O and H₂O⁺ + O₂ product channels are experimentally measured at 16 different excitation energies. State-resolved photodissociation mechanisms of the parent [O₂-H₂O]⁺ are interpreted as (1) the O₂(X³Σ_g^-) + H₂O⁺(X~2B1), O₂(a¹Δ_g) + H₂O⁺(X~2B1), and O₂(X³Σ_g^-) + H₂O⁺(A~2A1) channels are produced from direct dissociation of [O₂-H₂O]⁺ in its excited B~2A″, D~2A″, and F~2A″ states, respectively; (2) the O₂⁺(X²Π_g) + H2O(X~A11) channel is produced from nonadiabatic relaxations of the excited B~2A″, D~2A″, and F~2A″ states to the X~2A″ ground state with subsequent dissociation. The latter nonadiabatic processes involve charge-transfer on the potential energy surfaces, and the charge-transfer probabilities are determined from experimental results. The dissociation energy of the ground state to the lowest dissociation limit is experimentally refined as D₀ = 1.05 ± 0.05 eV. This work provides important information to understand the charge-transfer dynamics in the photochemistry of [O₂-H₂O]⁺ and in the ion-molecule reaction O₂ + H₂O⁺ → O₂⁺ + H₂O.

Photodissociation processes of a water–oxygen complex cation studied by an ion imaging technique

Photodissociation dynamics of O₂⁺–H₂O in the visible and ultraviolet regions was studied by ion imaging experiments and theoretical calculations.

Kinetics of the reaction of CO3˙−(H2O)n, n = 0, 1, 2, with nitric acid, a key reaction in tropospheric negative ion chemistry

One water molecule accelerates the reaction of CO₃˙⁻ with HNO₃, while two water molecules quench the reactivity.

Hydration Leads to Efficient Reactions of the Carbonate Radical Anion with Hydrogen Chloride in the Gas Phase

The carbonate radical anion CO₃^•- is a key intermediate in tropospheric anion chemistry. Despite its radical character, only a small number of reactions have been reported in the literature. Here we investigate the gas-phase reactions of CO₃^•- and CO₃^•-(H₂O) with HCl under ultrahigh vacuum conditions. Bare CO₃^•- forms OHCl^•- with a rate constant of 4.2 × 10^-12 cm³ s^-1, which corresponds to an efficiency of only 0.4%. Hydration accelerates the reaction, and ligand exchange of H₂O against HCl proceeds with a rate of 2.7 × 10^-10 cm³ s^-1. Quantum chemical calculations reveal that OHCl^•- is best described as an OH^• hydrogen bonded to Cl^-, while the ligand exchange product is Cl^-(HCO₃^•). Under tropospheric conditions, where CO₃^•-(H₂O) is the dominant species, Cl^-(HCO₃^•) is efficiently formed. These reactions must be included in models of tropospheric anion chemistry.

Vibronic coupling in the superoxide anion: the vibrational dependence of the photoelectron angular distribution

We present a comprehensive photoelectron imaging study of the O(2)(X  (3)Σ(g)(-),v(')=0-6)←O(2)(-)(X  (2)Π(g),v(")=0) and O(2)(a (1)Δ(g),v(')=0-4)←O(2)(-)(X  (2)Π(g),v(")=0) photodetachment bands at wavelengths between 900 and 455 nm, examining the effect of vibronic coupling on the photoelectron angular distribution (PAD). This work extends the v(')=1-4 data for detachment into the ground electronic state, presented in a recent communication [R. Mabbs, F. Mbaiwa, J. Wei, M. Van Duzor, S. T. Gibson, S. J. Cavanagh, and B. R. Lewis, Phys. Rev. A 82, 011401(R) (2010)]. Measured vibronic intensities are compared to Franck-Condon predictions and used as supporting evidence of vibronic coupling. The results are analyzed within the context of the one-electron, zero core contribution (ZCC) model [R. M. Stehman and S. B. Woo, Phys. Rev. A 23, 2866 (1981)]. For both bands, the photoelectron anisotropy parameter variation with electron kinetic energy, β(E), displays the characteristics of photodetachment from a d-like orbital, consistent with the π(g)(∗) 2p highest occupied molecular orbital of O(2)(-). However, differences exist between the β(E) trends for detachment into different vibrational levels of the X  (3)Σ(g)(-) and a (1)Δ(g) electronic states of O(2). The ZCC model invokes vibrational channel specific "detachment orbitals" and attributes this behavior to coupling of the electronic and nuclear motion in the parent anion. The spatial extent of the model detachment orbital is dependent on the final state of O(2): the higher the neutral vibrational excitation, the larger the electron binding energy. Although vibronic coupling is ignored in most theoretical treatments of PADs in the direct photodetachment of molecular anions, the present findings clearly show that it can be important. These results represent a benchmark data set for a relatively simple system, upon which to base rigorous tests of more sophisticated models.

Experimental and theoretical characterization of H(2)OOO(+)

This report presents the preparation and characterization of H2OOO+, an important intermediate in water-oxygen chemistry. The H2OOO+ cation was produced by co-deposition of H2O/Ar with radio frequency discharged O2/Ar at 4 K and was identified by four fundamental infrared absorptions. Quantum chemical calculations indicate a doublet ground state with a H2O-O2 hemi-bonded Cs structure.