An Extended Mixed Quantum/Classical Approach for Quantitative Calculation of Complex Refractive Index.

Area of Science:

• Physical Chemistry
• Spectroscopy
• Computational Chemistry

Background:

• The mixed quantum/classical approach is established for infrared spectral line shapes of water (H₂O).
• Quantitative spectral intensity calculations using this method have been limited, hindering direct experimental comparison.
• Previous methods used a normalized ordinate, restricting quantitative analysis.

Purpose of the Study:

• To extend the mixed quantum/classical framework for direct computation of water's complex refractive index.
• To enable accurate quantitative calculation of spectral intensity for infrared spectra of water.
• To facilitate direct comparisons between theoretical calculations and experimental spectral data.

Main Methods:

• Extended the mixed quantum/classical theoretical framework.
• Implemented direct computation of the full complex refractive index.
• Focused on the OH stretching region of H₂O spectra.

Main Results:

• The extended approach successfully captures both spectral shapes and intensities for H₂O.
• Inclusion of the local field effect was found to be crucial for accurate spectral intensity reproduction.
• The method allows for precise quantitative analysis of spectral intensity.

Conclusions:

• The enhanced theoretical framework provides accurate spectral intensity calculations for water.
• This advancement is vital for direct comparison of theoretical and experimental infrared spectra.
• The approach opens new avenues for analyzing bulk, thin-film, and cluster spectra of water.