Water dimer radical cation: structures, vibrational frequencies, and energetics

Area of Science:

• Computational Chemistry
• Physical Chemistry
• Quantum Chemistry

Background:

• The water dimer radical cation, (H2O)2+, is a key species in atmospheric and interstellar chemistry.
• Understanding its structure and energetics is crucial for modeling related chemical processes.

Purpose of the Study:

• To comprehensively characterize the potential energy surface of the water dimer radical cation in its doublet electronic state.
• To identify and analyze stable isomers, transition states, and other stationary points.

Main Methods:

• High-level ab initio calculations using coupled cluster theory with single and double excitations (CCSD) and CCSD with perturbative triple excitations [CCSD(T)].
• Employment of Dunning's correlation consistent polarized valence basis sets (cc-pVXZ and aug-cc-pVXZ, X = D, T, Q).
• Characterization of fourteen stationary points, including local minima and transition states.

Main Results:

• Two local minima were identified: a hydrogen-bonded isomer (1) and a hemibonded isomer (7).
• The adiabatic ionization energy for isomer 1 (10.81 eV) closely matches experimental values.
• The energy barrier for interconversion between isomers 1 and 7 is 15.1 kcal mol(-1), with a separation of 8.8 kcal mol(-1).

Conclusions:

• The study provides a detailed map of the water dimer radical cation's potential energy surface.
• The calculated properties, including ionization energies and dissociation energies, offer valuable data for experimental validation and theoretical comparisons.
• The findings contribute to a deeper understanding of water cluster cation behavior and their role in chemical systems.