ACCURATE AB INITIO POTENTIAL SURFACES OK AR-HF, $AR-H_{2}O$, AND $AR-NH_{3}$
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Date
1994
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Ohio State University
Abstract
We present accurate potential energy surface for Ar--HF, $Ar--H_{2}O$, and $Ar--NH_{3}$ from the supermolecular calculations using M\""{o} Sller-Plesset perturbation theory up to the complete fourth-order (MP4) and efficient basis sets containing bond functions. The calculations on Ar-HF with a fixed HF bond length of $r = [r)_{\nu=0}$ give a global potential minimum with a well depth of $200.0 cm^{-1}$ at the position $R = 3.470 {\AA}, \theta = 0^{\circ}$ (linear Ar-H-F) a secondary minimum with a well depth of $881. cm^{-1}$ at $R=3.430 {\AA} \theta = 180^{\circ}$ (linear Ar-F-H) and a potential barrier f $128.3 cm^{-1}$ that separates the two minima near $R=3.555 {\AA}, =90^{\circ}$ (T shaped). Further calculations on the three main configurations of Ar-HF with varying HF bond length are carried out to obtain vibrationally averaged well depths for $\nu$ =0,1,2 ad 3. Our primary wells are about $15 cm^{-1}$ higher than those of Hutson’s H6(4,3,2) $potential^{1}$ for $\nu$ =0,1,2 ad 3, and our minimum distances are about 0.05 {\AA} longer. The intermolecular potentials of $Ar-H_{2}O$ and $Ar-NH_{3}$ are calculated with the monomers held fixed at equilibrium geometry. The calculations on $Ar-H_{2}O$ give a single global minimum with a well depth of $130.2 cm^{-1}$ at $R=3.603 {\AA}, \nu = 75^{\circ}, \theta = 0^{\circ}$, along with barriers of 22.6 and $26.6 cm^{-1}$ for in-plane rotaion at $\theta=0^{\circ}$, and $180^{\circ}$ respectively, and a barrier of $52.6 cm^{-1}$ for out-of-plane rotation at $\theta = 90^{\circ}, \theta = 90^{\circ}$. All these agree well with experiment, especially with the recent AW2 $potential.^{2}$ The calculations on $Ar-NH^{3}$ give a single global minimum with a well depth of $130.1 cm^{-1}$ at $R=3.628 {\AA}, \theta =90^{\circ}$. All these agree well with experiment, especially with the recent AW2 $potential.^{2}$ The calculations on $Ar-NH_{3}$ give a single global minimum with a well depth of $130.1 cm^{-1}$ at $R=3.628 {\AA}, \theta =90^{\circ}, \theta = 60^{\circ}$, along with barriers of 55.2 and $38.0 cm^{-1}$ for end-over-end rotation at $\theta = 0^{\circ}$ and $180^{\circ}$ respectively, and a barrier of $26.6 cm^{-1}$ for rotation about $NH^{3}$ symmetry axis at $\theta =90^{\circ}, \phi = 0^{\circ}$. Again, all these agree with $experiment.^{3}$
Description
1. J.M. Hutson, J. Chem, Phys 96, 6752 (1992). 2. R.C. Cohen and R.J. Saykally, J. Chem. Phys, 98, 1007 (1993). 3. C.A. Schmuttenmaer, R. Cohen, and R.J. Saykally, J. Chem. Phys., submitted.
Author Institution: Department of Chemistry, Harvard University
Author Institution: Department of Chemistry, Harvard University