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

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 $\text{A˚}$ 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.