Ultrafast 2D-IR spectroscopy of intensely optically scattering pelleted solid catalysts

Area of Science:

• Materials Science
• Spectroscopy
• Physical Chemistry

Background:

• Powdered solid samples are typically analyzed using infrared (IR) spectroscopy via compressed pellets.
• Light scattering from these pellets significantly hinders advanced techniques like two-dimensional (2D)-IR spectroscopy.
• Developing methods to overcome scattering is crucial for detailed material characterization.

Purpose of the Study:

• To present an experimental approach for obtaining high-quality 2D-IR spectra from scattering powdered samples.
• To enable 2D-IR analysis of materials like zeolites, titania, and fumed silica under various conditions.
• To investigate and mitigate issues related to laser heating in 2D-IR spectroscopy.

Main Methods:

• Utilized a combination of phase cycling and polarization control for scatter suppression.
• Employed a bright probe laser beam, comparable in strength to the pump beam, for enhanced scatter reduction.
• Conducted experiments on zeolites, titania, and fumed silica in the OD-stretching region.
• Performed measurements under flowing gas and variable temperatures up to ~500°C.

Main Results:

• Successfully acquired high-quality 2D-IR spectra from scattering pellets.
• Demonstrated effective scatter suppression using the proposed bright probe laser technique.
• Analyzed nonlinear optical signals and found them to be limited.
• Discussed the impact of steady-state and transient laser heating effects.

Conclusions:

• The developed experimental approach enables high-quality 2D-IR spectroscopy on scattering powdered samples.
• The method is effective for various materials and conditions, including high temperatures.
• Understanding and managing laser heating effects are important for practical applications of this technique.