Thermal Population Fluctuations in Two-Dimensional Infrared Spectroscopy Captured with Semiclassical Mechanics

Area of Science:

• Chemical Physics
• Spectroscopy
• Condensed Matter Physics

Background:

• Vibrational modes in molecules are influenced by their surrounding solvent environment.
• Understanding these interactions is crucial for comprehending molecular dynamics in condensed phases.
• Multidimensional vibrational spectroscopy offers a powerful tool to probe these complex interactions.

Purpose of the Study:

• To investigate the influence of solvent-driven thermal fluctuations on vibrational mode populations.
• To demonstrate the capability of time-resolved two-dimensional (2D) infrared spectroscopy in revealing inter-modal coupling.
• To validate a semiclassical computational method for simulating complex vibrational dynamics.

Main Methods:

• Time-resolved two-dimensional (2D) infrared spectroscopy was employed to study solvated carbon dioxide (CO2).
• The optimized mean-trajectory (OMT) method, a trajectory-based semiclassical approach, was used for computational analysis.
• Simulations involved coupled anharmonic modes with stochastic energy transitions to mimic solvent effects.

Main Results:

• Distinct spectral features corresponding to ground- and excited-state thermal populations of bend modes were observed.
• Time-dependence of spectral peaks was linked to solvent-driven thermal fluctuations in lower-frequency bend modes.
• The OMT calculation successfully reproduced the impact of thermal fluctuations on the 2D spectrum.

Conclusions:

• Multidimensional vibrational spectroscopy effectively reveals interactions among vibrational modes in condensed phases.
• Solvent-driven fluctuations significantly influence vibrational energy landscapes.
• The OMT method provides a reliable semiclassical approach for simulating complex spectroscopic phenomena.