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

Azzedine Lakhlifi (1) , Pierre-Richard Dahoo (2)

1 UTINAM - Univers, Transport, Interfaces, Nanostructures, Atmosphère et environnement, Molécules (UMR 6213)
2 PLANETO - LATMOS

The infrared bar-spectrum of a single ammonia molecule encapsulated in nano-cage C₆₀ fullerene molecule is modeled using the site inclusion model successfully applied to analyze spectra of CO₂ isotopologues isolated in rare gas matrix. Calculations show that NH₃ can rotate freely on a sphere of radius 0.184 Å around the site center of the nano-cage and spin freely about its C₃ symmetry axis. In the static field inside the cage degenerate ν₃ and ν₄ vibrational modes are blue shifted and split. When dynamic coupling with translational motion is considered, the spectral signature of the ν₂ 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.

Domaines: Chimie théorique et/ou physique

Azzedine Lakhlifi, Pierre-Richard Dahoo. Enhanced localization of tunneling of the NH₃ umbrella mode in nano-cage fullerene. Chemical Physics, 2011, 386 (1-3), pp.73-80. ⟨10.1016/j.chemphys.2011.06.005⟩. ⟨hal-00627556⟩