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

Area of Science:

• Physical Chemistry
• Chemical Physics
• Spectroscopy

Background:

• The [O₂-H₂O]⁺ complex plays a role in atmospheric and interstellar chemistry.
• Understanding its photodissociation provides insights into ion-molecule reactions and energy transfer processes.

Purpose of the Study:

• To experimentally investigate the photodissociation dynamics of the [O₂-H₂O]⁺ ion.
• To elucidate the mechanisms, including direct dissociation and nonadiabatic processes involving charge transfer.
• To determine the branching ratios, kinetic energy release, and dissociation energy of the complex.

Main Methods:

• Utilized a cryogenic ion trap velocity map imaging spectrometer for mass-selected, internally cold ions.
• Employed time-of-flight mass spectrometry and velocity map imaging to detect O₂⁺ and H₂O⁺ photofragments.
• Measured branching ratios and kinetic energy release distributions at 16 different excitation energies (580-266 nm).

Main Results:

• Identified direct dissociation pathways yielding O₂ + H₂O⁺ and O₂⁺ + H₂O.
• Observed nonadiabatic processes involving charge transfer leading to O₂⁺ + H₂O products.
• Experimentally refined the dissociation energy of the ground state to D₀ = 1.05 ± 0.05 eV.

Conclusions:

• The study clarifies the state-resolved photodissociation mechanisms of [O₂-H₂O]⁺.
• Provides quantitative information on charge-transfer probabilities in the dissociation process.
• Offers crucial data for understanding the O₂ + H₂O⁺ ion-molecule reaction.