https://doi.org/10.1007/s100530050029
A theoretical spectroscopic study of single ammonia molecules adsorbed on the surface of fcc-type argon clusters. Surface effects on the ν2 vibration-inversion mode
Laboratoire d'Astrophysique de l'Observatoire de Besançon (UPRES
A CNRS 6091) , 41 bis avenue de l'Observatoire, B.P. 1615, Université
de Franche-Comté, 25010 Besançon Cedex, France
Corresponding author: a azzedine.lakhlifi@obs-besancon.fr or iut-bm.univ-fcomte.fr
Received:
6
April
1999
Revised:
19
July
1999
Published online: 15 February 2000
Ammonia monomers have been adsorbed on argon clusters at low temperature
K by Rohmund and Huisken [CITE] using the pick-up
technique. They measured the spectrum of the NH3 molecules in the region
of the 
umbrella mode. Two broad bands centered around 970 and 1000 cm-1
with finer details were observed. The authors attempted to
interpret the obtained spectrum on the basis of the free rotation motions of
the molecules. In this paper semi-empirical atom-atom potential energy
calculations are performed for the ammonia monomer adsorbed on a rigid
face-centered-cubic (fcc)-type surface of the argon cluster. In the
equilibrium position of the rigid molecule on the cluster surface the
orientational potential energy surface exhibits two quasi-equivalent minima
separated by a potential barrier of about 100 cm-1. The symmetry of the
molecular vibration-inversion double-well potential is destroyed; the
inversion motion is then forbidden in the ground state. On the basis of the
two adsorption orientations, the vibrational frequency shifts are calculated
and the obtained infrared bar-spectrum agrees with the experimental one.
PACS: 33.20.-t – Molecular spectra / 33.20.Ea – Infrared spectra / 33.20.Vq – Vibration-rotation analysis
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2000
