Electronic structure of the water dimer cation.

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Spectroscopy

Background:

• Proton transfer in water dimer cations is a fundamental process.
• Understanding electronic state changes is crucial for reaction dynamics.

Purpose of the Study:

• Investigate spectroscopic signatures of proton transfer in (H2O)2+.
• Characterize electronic states along the proton transfer coordinate.
• Evaluate computational methods for studying these systems.

Main Methods:

• Equation-of-motion coupled-cluster with single and double substitutions (EOM-CC2) for ionized systems.
• Qualitative molecular orbital theory for state analysis.
• Ab initio calculations to assess density functional theory (DFT) performance.

Main Results:

• Proton transfer causes substantial changes in the electronic spectrum of (H2O)2+.
• Electronic spectra exhibit local excitations and charge-transfer bands.
• A self-interaction corrected DFT/BLYP method accurately predicts isomer energetics.

Conclusions:

• Time-resolved electronic femtosecond spectroscopy is suitable for monitoring ionization dynamics in water dimer cations.
• The corrected DFT/BLYP method shows promise for larger systems.