Infrared Optical Functions of Water Retrieved Using Attenuated Total Reflection Spectroscopy

Area of Science:

• Spectroscopy
• Optical Physics
• Materials Science

Background:

• Infrared spectroscopy is crucial for material characterization.
• Accurate retrieval of optical functions is essential for understanding material properties.
• Existing methods for optical function retrieval can be complex, especially for materials with strong dispersion and absorption.

Purpose of the Study:

• To develop and validate a comprehensive modeling methodology for non-polarized infrared attenuated total reflection (IR-ATR) spectra.
• To demonstrate the method's applicability for retrieving optical functions of isotropic materials, including those with strong dispersion and absorption.
• To evaluate the accuracy of the method by analyzing liquid water spectra.

Main Methods:

• Modeling IR-ATR spectra using Fresnel equations.
• Employing wavenumber-dependent dielectric function models for isotropic materials.
• Analyzing spectra obtained with diamond and germanium internal reflection elements in the 100-4400 cm⁻¹ region.

Main Results:

• The developed modeling scheme provides a suitable and easy methodology for retrieving optical functions.
• The method proved effective even for spectral regions with strong dispersion and absorption resonances.
• Computed refractive index of water from dispersion analysis showed good agreement with literature data.

Conclusions:

• Comprehensive modeling based on Fresnel equations is a robust and accessible approach for IR-ATR spectral analysis.
• The methodology is general and applicable to a wide range of isotropic materials.
• The study validates the accuracy of the method for determining optical properties of liquids like water.