Angle-Resolved Electron Scattering from H_{2}O near 0°.

Area of Science:

• Atomic and Molecular Physics
• Electron Scattering
• Quantum Chemistry

Background:

• Accurate electron scattering cross sections for water are crucial for understanding its atmospheric chemistry and radiation interactions.
• Previous experimental data for water (H₂O) scattering cross sections have shown discrepancies, particularly at lower energies.
• Theoretical models, such as ab initio R-matrix calculations, require experimental validation.

Purpose of the Study:

• To precisely measure the total electron scattering cross section of water (H₂O) in the energy range of 3-100 eV.
• To investigate forward electron scattering from water at angles between 0° and 3.5°.
• To provide experimental data for validating theoretical predictions, particularly ab initio R-matrix calculations.

Main Methods:

• Utilized an electron beam with high angular discrimination (approximately 0.7°) for measurements.
• Measured the total (elastic plus inelastic) cross section for H₂O across a broad energy range.
• Probed forward scattering by measuring differential elastic cross sections at a scattering angle of approximately 1° for energies up to 12 eV.

Main Results:

• Observed broad coincidence with recent experimental data, including a distinct shoulder in the 6-12 eV energy region.
• Found that cross sections at energies below 6 eV were approximately 30% higher than some previous measurements.
• Experimental results for forward scattering were found to be within one standard deviation of corresponding ab initio R-matrix calculations.

Conclusions:

• The study provides new, high-precision measurements of electron scattering cross sections for water.
• The findings highlight discrepancies at low energies and validate theoretical predictions in previously unexplored forward scattering regions.
• This work serves as a critical experimental test for theoretical models of electron-water interactions.