Fifth Electronic Computational Chemistry Conference
ECCC5 2nd November - 30th November 1998
VIBRATIONS and VRT DYNAMICS of the AMMONIA DIMER : A FURTHER ANALYSIS.
Francis F. MUGUET
Laboratoire de Mathématiques Appliquées (L.M.A)
E.N.S.Techniques Avancées
32 Boulevard Victor 75739 PARIS Cedex
FRANCE
and
Applications Scientifiques du Calcul Intensif ( ASCI)
UPR
CNRS 9049
Bat. 506 Campus d'Orsay
91403 ORSAY
FRANCE
M. P. BASSEZ
Laboratoire de Chimie Physique
I.U.T Strasbourg-Sud,
Université de Strasbourg III.
72 Route du Rhin, 67400 Illkirch-Graffenstaden
FRANCE
ABSTRACT
The ammonia dimer presents a very interesting challenge in computational
chemistry.
Ab initio methods have much difficulties in predicting correctly its
geometry.
With the help a new BSSE correction scheme
[Muguet 95A] , we predicted as the
global minimum an asymmetric geometry. This structure is similar to the one deduced
from the experimental VRT spectra, assuming rigid monomers
[Olthof 94A] .
The RHF hessian was computed at this asymmetric geometry
[Muguet 95B] .
After analysis of the vibration
modes, we concluded
that monomer inversions might be quenched in the dimer.
Instead,
splittings which were previously assigned to monomer inversion
[Olthof 94B] , should be assigned to
some interchange tunneling dynamics.
In this paper,the MCSCF Hessian is computed, at
the asymmetric geometry.
Isotopic substitutions are performed and related frequencies are reported.
Vibrational motions are
analyzed with the help of animations, to better understand the rather complex
and unusual VRT dynamics of the ammonia dimer.
