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Vibrational coherence transfer characterized with Fourier-transform 2D IR spectroscopy
M Khalil1, N Demirdöven, A Tokmakoff
1Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139.
The Journal of Chemical Physics
|July 21, 2004
Summary
This study reveals how vibrational coherence transfers between carbonyl ligands in a rhodium complex, influencing molecular dynamics. Understanding this transfer is key for analyzing complex molecular structures using two-dimensional infrared spectroscopy.
Area of Science:
- Physical Chemistry
- Spectroscopy
- Molecular Dynamics
Background:
- Two-dimensional infrared (2D IR) spectroscopy is a powerful technique for studying ultrafast molecular dynamics.
- Vibrational coherence and its transfer are crucial phenomena in multilevel vibrational systems.
Purpose of the Study:
- To investigate vibrational coherence transfer, dephasing, and population relaxation in a multilevel vibrational system.
- To understand the influence of coherence transfer on 2D IR spectral features and structural analysis.
Main Methods:
- Utilized two-dimensional infrared (2D IR) spectroscopy to study the C[Triple Bond]O stretching vibrations of Rh(CO)(2)acac in hexane.
- Modeled the vibrational dynamics using density matrix propagation with the Redfield equation, incorporating relaxation and reorientation effects.
Main Results:
- Observed relaxation-induced peaks in 2D IR spectra, directly linked to coherence transfer rates between vibrational frequencies.
- Determined coherence and population transfer time scales between symmetric and asymmetric CO stretches to be 350 fs and 3 ps, respectively.
- Demonstrated that coherence transfer impacts the analysis of structural variables from 2D IR spectroscopy.
Conclusions:
- Coherence transfer, driven by interactions between carbonyl stretches and dark states (d-pi(*) back bonding), significantly influences 2D IR spectral dynamics.
- The study provides insights into modeling vibrational relaxation processes and their effect on spectral interpretation.
- Established time scales for coherence and population transfer, crucial for understanding molecular dynamics in transition metal carbonyl complexes.