Trapping effects on the vibration-inversion-rotation motions of an ammonia molecule encapsulated in C$_{60}$ fullerene molecule

TL;DR

This study models the infrared spectrum of an ammonia molecule inside a C60 fullerene, revealing how encapsulation affects vibrational and rotational motions, with potential for temperature sensing applications.

Contribution

It introduces a site inclusion model for ammonia in C60, analyzing its vibrational and rotational behaviors and their spectral signatures within the nano-cage.

Findings

Ammonia can rotate freely inside C60 with a radius of 0.184 Å.

Vibrational modes are shifted and split due to the cage environment.

Spectral changes can be used to determine surrounding media temperature.

Abstract

The infrared bar-spectrum of a single ammonia molecule encapsulated in nano-cage C$_{60}$ fullerene molecule is modelled using the site inclusion model successfully applied to analyze spectra of CO$_2$ isotopologues isolated in rare gas matrix. Calculations show that NH$_3$ can rotate freely on a sphere of radius 0.184 $\text{\AA}$ around the site centre of the nano-cage and spin freely about its C$_3$ symmetry axis. In the static field inside the cage degenerate $\nu_3$ and $\nu_4$ vibrational modes are blue shifted and split. When dynamic coupling with translational motion is considered, the spectral signature of the $\nu_2$ mode is modified with a higher hindering barrier (2451 cm$^{-1}$), an effective reduced mass (6.569 g.mol$^{-1}$) and a longer tunneling time (55594 ps) for the fundamental level compared to gas-phase values (2047 cm$^{-1}$), (2.563 g.mol$^{-1}$) and (20.85 ps). As a result this mode is red shifted. Moreover, simulation shows that the changes in the bar-spectrum of the latter mode can be used to probe the temperature of the surrounding media in which fullerene is observed.