AC/DC Analysis: Broad and Comprehensive Approach to Analyze Infrared Intensities at the Atomic Level.

Area of Science:

• Computational Chemistry
• Molecular Spectroscopy
• Quantum Chemistry

Background:

• Infrared (IR) spectroscopy is crucial for understanding molecular structure and dynamics.
• Assigning specific atomic contributions to IR intensities is challenging.
• Existing methods lack a comprehensive approach to partition IR intensity.

Purpose of the Study:

• To present a complete theoretical protocol for partitioning infrared intensities into atomic contributions.
• To introduce two complementary approaches: atomic contributions (ACs) and dynamic contributions (DCs).
• To provide a robust framework for detailed analysis of molecular vibrational spectroscopy.

Main Methods:

• Developed the AC/DC analysis framework to partition total IR intensity.
• Utilized population analysis models (CCTDP/CCT) for further partitioning.
• Demonstrated invariance to rotation and translation for broad applicability.
• Ensured compatibility with various charge models reproducing the molecular dipole moment.

Main Results:

• The AC/DC analysis provides complementary perspectives on IR intensity origins.
• The partitioning conserves key features of the total IR intensity.
• Numerical results support the theoretical interpretation and practical application.
• The protocol is applicable to molecules of any size, shape, or symmetry.

Conclusions:

• The AC/DC analysis offers a powerful, versatile tool for interpreting IR spectra.
• The method provides atom-specific insights into molecular vibrational behavior.
• A fully automated protocol using the Placzek program is available for researchers.