Understanding the Dynamics of Kr@C$_{60}$ : A Far-Infrared Vibrational Study

The C$_{60}$ molecule has remarkable ability to encapsulate atoms inside the hollow carbon cage. Here, we report a high-resolution far infrared spectral investigation of endohedral Kr@C$_{60}$. Unexpected softening of the T$_{1u}$(1) mode ($\sim$528 cm$^{-1}$) and sharp peak at $\sim$600 cm$^{-1}$ have been observed throughout the temperature range of investigation. The response of Kr@C$_{60}$ is compared to that of pristine C$_{60} $, and the spectral differences are discussed in terms of local symmetry and prospects of Kr@C$_{60}$ as a building block for organic superconductors.