Infrared spectroscopy of small-molecule endofullerenes

Area of Science:

• Physical Chemistry
• Supramolecular Chemistry
• Spectroscopy

Background:

• Endohedral fullerenes, such as H₂@C₆₀, involve encapsulating molecules within fullerene cages.
• Confinement alters the encapsulated molecule's properties, including its translational and rotational dynamics.
• Infrared (IR) spectroscopy is a powerful tool for probing molecular vibrations and motions.

Purpose of the Study:

• To investigate the dynamics of hydrogen isotopologues (H₂, D₂, HD) encapsulated within the C₆₀ fullerene cage.
• To understand how confinement within C₆₀ influences the translational and rotational motion of hydrogen.
• To derive parameters describing the potential energy surface and dipole moment of H₂@C₆₀ from experimental data.

Main Methods:

• Infrared (IR) spectroscopy was employed to study H₂, D₂, and HD encapsulated in C₆₀.
• Analysis of absorption spectra focused on side bands related to translational and rotational modes.
• A model of a vibrating rotor in a 3D spherical potential was used to interpret the spectral data.

Main Results:

• Quantized translational motion and correlated rotation of hydrogen were observed within the C₆₀ cavity.
• IR absorption spectra revealed side bands associated with hydrogen's vibrational, rotational, and translational modes.
• Parameters for the potential energy surface and dipole moment of H₂@C₆₀ were derived from the spectral analysis.
• Predicted energies for H₂@C₇₀ were compared with experimental low-temperature IR spectra.

Conclusions:

• Confinement in C₆₀ induces significant changes in hydrogen's dynamic behavior, including quantized translation and IR activity.
• The derived potential energy surface parameters accurately describe the H₂-C₆₀ interaction.
• The study provides a foundation for predicting and analyzing the properties of other endohedral fullerene complexes, such as H₂@C₇₀.