Enhanced localization of tunneling of the NH3 umbrella mode in nano-cage fullerene

► We model the infrared bar-spectrum of ammonia trapped in a C60 fullerene molecule. ► We examine in detail the interaction potential energy experienced by NH3 in the C60. ► Simultaneous orientation and center of mass translation motions of NH3 lead to free rotation level scheme with modified rotational constant. ► The vibration-inversion mode (umbrella mode) of NH3 is drastically modified.