Two-dimensional electronic spectroscopy of anharmonic molecular potentials.

Area of Science:

• Physical Chemistry
• Spectroscopy
• Quantum Dynamics

Background:

• Two-dimensional electronic spectroscopy (2DES) probes coupled electron-phonon dynamics.
• The influence of anharmonicities in nuclear potentials on 2DES spectra remains largely unexplored, particularly for strong coupling regimes.

Purpose of the Study:

• To investigate the effects of anharmonicities in electron-phonon coupling on two-dimensional electronic spectroscopy (2DES) spectra.
• To identify and characterize spectral features unique to 2DES arising from nuclear anharmonicities.

Main Methods:

• Theoretical modeling using a two-level system.
• Simulations employing displaced harmonic oscillators with differing curvatures and displaced Morse oscillators.
• Analysis of spectral features including zero-phonon lines, diagonal and cross-peaks, and symmetry properties.

Main Results:

• Anharmonicities transfer the zero-phonon line shape to the diagonal of 2DES spectra.
• Horizontal mirror-symmetry is broken in the 2DES spectra at long waiting times due to anharmonicities.
• Novel anharmonic effects identified include cross-peak twisting and oscillation period mismatches or chaotic oscillations in stimulated emission signals.

Conclusions:

• Anharmonicities introduce distinct signatures in 2DES spectra, differing from linear spectroscopy observations.
• The findings provide a framework for interpreting more realistic 2DES signals beyond simple harmonic models.
• This work enhances the understanding and application of 2DES for studying complex molecular dynamics.