Infrared spectrum and structural assignment of the water trimer anion

Area of Science:

• Physical Chemistry
• Spectroscopy
• Quantum Chemistry

Background:

• The water trimer anion ((H2O)n(-)) is a key system for understanding electron-solvation in water clusters.
• Previous studies on smaller and larger water cluster anions established electron binding mechanisms.

Purpose of the Study:

• To experimentally measure the bending vibrational spectrum of the perdeuterated water trimer anion ((D2O)3(-)).
• To computationally investigate the structure and vibrational spectra of (D2O)3(-) using various electronic structure methods.
• To determine the most stable isomer and the electron binding site within the water trimer anion.

Main Methods:

• Infrared (IR) spectroscopy was used to measure the OD bending vibrational spectrum of (D2O)3(-).
• Electronic structure calculations were performed using MP2, CCSD, and Becke3LYP methods.
• Comparison of experimental spectra with calculated spectra for different isomers.

Main Results:

• The experimental spectrum was limited to the OD bending region due to the low electron binding energy (~150 meV).
• Calculations indicated that a chain isomer, with three water molecules in a line, best matched the experimental spectrum.
• The excess electron in the chain isomer is primarily bound to a terminal water monomer, with two dangling OD groups.

Conclusions:

• The chain isomer is the most likely structure for the water trimer anion.
• The electron binding mechanism involves localization on a terminal water molecule, consistent with previous findings for other water cluster anions.
• The study provides insights into the structure and electron binding properties of water cluster anions.