Multimode vibrational dynamics and orientational effects in fluorescence-encoded infrared spectroscopy. I. Response...

Area of Science:

• Chemical Physics
• Spectroscopy
• Molecular Dynamics

Background:

• Fluorescence-encoded infrared (FEIR) spectroscopy is an emerging technique for high-sensitivity vibrational spectroscopy in solution.
• FEIR experiments utilize ultrashort pulses for time-resolved excitation of electronic and vibrational transitions.
• The technique is sensitive to ground-state vibrational dynamics, vibronic coupling, and transition dipole orientations.

Purpose of the Study:

• To develop a theoretical treatment of FEIR spectroscopy for understanding complex molecular phenomena.
• To describe Fourier-transform FEIR experiments using a nonlinear response function for a two-level electronic system coupled to vibrations.
• To interpret experimental FEIR measurements by analyzing vibrational coherence and orientational effects.

Main Methods:

• Development of a nonlinear response function for Fourier-transform FEIR spectroscopy.
• Theoretical modeling of a two-level electronic system coupled to multiple vibrations.
• Analysis of vibrational coherence, population response, and orientational contributions to the spectra.

Main Results:

• Vibrational coherence between modes creates oscillatory features that distort FEIR spectra.
• The interference patterns depend on the relative signs of Franck-Condon wavefunction overlaps.
• Polarization-dependent experiments can extract information on relative transition dipole angles.

Conclusions:

• The theoretical framework provides a comprehensive understanding of FEIR spectroscopic information.
• The study aids in interpreting experimental data and optimizing FEIR experimental design.
• This work establishes a foundation for advanced applications of FEIR spectroscopy in molecular science.