Continuous probing of cold complex molecules with infrared frequency comb spectroscopy

Area of Science:

• Molecular Spectroscopy
• Physical Chemistry
• Quantum Dynamics

Background:

• High-resolution infrared spectroscopy is vital for molecular studies but limited to small systems due to spectral congestion.
• Existing techniques face trade-offs between bandwidth, acquisition time, sensitivity, and resolution.
• Cavity-enhanced direct frequency comb spectroscopy (CE-DFCS) offers broad bandwidth and high resolution but still struggles with spectral congestion.

Purpose of the Study:

• To overcome spectral congestion in infrared spectroscopy for larger, more complex molecules.
• To develop a method for acquiring rotationally resolved spectra of challenging molecular systems.
• To expand the scope of molecules accessible to high-resolution infrared spectroscopic analysis.

Main Methods:

• Integration of buffer gas cooling with cavity-enhanced direct frequency comb spectroscopy (CE-DFCS).
• Production of continuous, cold molecular samples for enhanced spectral clarity.
• Acquisition of direct absorption spectra in the C-H stretching region.

Main Results:

• Successfully obtained rotationally resolved infrared spectra of nitromethane, a complex model system.
• Applied the technique to large organic molecules like naphthalene, adamantane, and hexamethylenetetramine.
• Demonstrated significant improvements in efficiency, spectral resolution, and specificity for complex molecule analysis.

Conclusions:

• The combined buffer gas cooling and CE-DFCS approach effectively resolves spectral congestion in large molecules.
• This technique significantly advances the study of complex molecular structures and dynamics.
• The method opens new avenues for investigating molecules of fundamental spectroscopic and astrochemical importance.