Resonance vibrational Raman optical activity: a time-dependent density functional theory approach

Area of Science:

• Computational Chemistry
• Molecular Spectroscopy
• Quantum Chemistry

Background:

• Vibrational Raman Optical Activity (VROA) is a powerful spectroscopic technique for determining molecular chirality.
• Accurate theoretical prediction of VROA spectra is crucial for experimental interpretation.
• Existing methods often simplify or neglect the influence of electronic excited state lifetimes on VROA calculations.

Purpose of the Study:

• To develop and present a novel computational method for calculating both on- and off-resonance VROA spectra.
• To extend existing VROA calculation methodologies by incorporating the finite lifetime of electronic excited states.
• To provide a more comprehensive theoretical framework for understanding and predicting VROA phenomena.

Main Methods:

• Utilizing time-dependent density functional theory (TD-DFT) within a short-time approximation for Raman scattering.
• Extending normal VROA calculations by including a damping term in linear response theory to account for finite excited state lifetimes.
• Employing gauge-origin independent methods (modified-velocity gauge or gauge-included atomic orbitals) for normal VROA and modified-velocity gauge for resonance VROA.

Main Results:

• The developed method successfully calculates both on- and off-resonance VROA spectra.
• The inclusion of excited state lifetimes refines the VROA calculations, particularly for resonance cases.
• Initial calculations for H(2)O(2) and (S)-methyloxirane show good agreement with theoretical predictions and provide insights into their VROA characteristics.

Conclusions:

• The presented TD-DFT based method offers an accurate and versatile approach for computing VROA spectra.
• Accounting for finite excited state lifetimes is essential for precise on-resonance VROA predictions.
• This work advances the theoretical capabilities for analyzing chiral molecules using VROA spectroscopy.