Multi-mode heterodyned 5th-order infrared spectroscopy.

Area of Science:

• Physical Chemistry
• Spectroscopy
• Molecular Dynamics

Background:

• Fifth-order multidimensional infrared (5D IR) spectroscopy is a powerful technique for probing molecular vibrations.
• Understanding energy transfer pathways in molecules is crucial for various chemical and biological processes.

Purpose of the Study:

• To investigate vibrational energy relaxation dynamics using 5D IR spectroscopy.
• To explore the capability of 5D IR spectroscopy in identifying specific energy transfer pathways.

Main Methods:

• Utilized a three-beam dual-frequency configuration for 5D IR spectroscopy with heterodyned detection.
• Acquired 5th-order cross peaks involving overtones and combination bands in 4-azidobutyrate-N-hydroxysuccinimide ester in solution.
• Analyzed waiting time dependences of 3rd and 5th order cross peaks.

Main Results:

• Detected numerous 5th-order cross peaks between spatially close and separated vibrational modes (up to 12 Å).
• Observed distinct waiting time dynamics for 3rd and 5th order cross peaks, indicating different relaxation pathways.
• Demonstrated that 5th-order signals are less sensitive to weakly coupled modes, enabling focus on strongly coupled ones.
• Constructed absorptive 5th-order cross peaks reporting on three-point correlation functions and mode coupling.

Conclusions:

• Fifth-order spectroscopy effectively distinguishes vibrational modes coupled to the reporter mode.
• This technique aids in identifying specific energy relaxation and transport pathways in molecules.
• The method offers a simple yet powerful approach for studying anharmonicity and molecular dynamics, with potential for broad applications.