Quantitative evaluation of IR and corresponding VCD spectra.

Area of Science:

• Spectroscopy and Molecular Physics
• Chiroptical Spectroscopy
• Computational Chemistry

Background:

• Classical electromagnetic theory provides a framework for understanding infrared (IR) and vibrational circular dichroism (VCD) spectra.
• Dispersion theory, extended by Born and Kuhn, quantitatively describes optical properties of chiral substances.
• IR and VCD spectra are shaped by dielectric function and chiral admittance functions.

Purpose of the Study:

• To apply dispersion analysis using coupled oscillators to model IR and VCD spectra.
• To quantitatively describe the dielectric function and chiral admittance functions for chiral compounds.
• To evaluate the sufficiency of a two-coupled-oscillator model for spectral analysis.

Main Methods:

• Utilized classical electromagnetic theory and dispersion analysis.
• Employed a coupled oscillator model with five parameters: oscillator strength, damping, oscillator position, vertical distance, and coupling constant.
• Analyzed experimental IR and VCD spectra of α-Pinene and Propylene oxide.

Main Results:

• Demonstrated that the area of positive and negative bands in wavenumber-normalized absorbance spectra are equal.
• The coupled oscillator model successfully described the dielectric and chiral admittance functions.
• A model with two coupled oscillators provided good agreement between experimental and modeled spectral data for most bands.

Conclusions:

• The coupled oscillator model is effective for analyzing and understanding IR and VCD spectra of chiral molecules.
• Dispersion analysis provides quantitative insights into the optical properties of chiral compounds.
• The study validates the use of classical electromagnetic theory and dispersion analysis in chiroptical spectroscopy.