A b i n i t i o potential energy surfaces of Ar–NH3 for different NH3 umbrella angles

Abstract

Four ab initio potential energy surfaces of the van der Waals system argon-ammonia are computed for the following four different HNH ( "umbrella" ) angles of ammonia: 100°, 106.67°, 113.34°, and 120°. These potentials have been obtained by Heitler-London short-range calculations and from multipole-expanded dispersion and induction long-range contributions. A Tang-Toennies-like damping is applied to the long-range energy. Each surface is given analytically in the form of a spherical harmonic expansion through 1 = 1, where the expansion functions depend on the polar angles of the argon atom with respect to the principal axes of N H 3. The expansion coefficients are represented by functions depending on the distance between the monomers. The potential for the equilibrium HNH angle 106.67° is applied to the computation of interaction virial coefficients in which quantum effects through fr are included.

Close coupling results for inelastic collisions of NH3 and Ar. A stringent test of a spectroscopic potential

“…This model surface contains long-range attractive forces of induction and disper sion and short range Coulombic and electron ex change repulsive forces. The long-range dispersion coefficients were taken from ab initio calculations [ 4,7 ], since they cannot be properly derived from ex periment. The three intermolecular coordinates (R , û, (p) were treated without invoking any approxima tion regarding their separability.…”

“…[4] and a second potential, in which the original ab initio potential contains one scaling parameter that was chosen to improve the agreement with the spec troscopic data [5]. This second potential proved to give better agreement with the measured scattering data as well.…”

Near-infrared spectrum and rotational predissociation dynamics of the He–HF complex from an ab initio symmetry-adapted perturbation theory potential

“…Moreover, only a few ab initio potentials have been checked by expos ing them to the severe test of computing the observed (highresolution) spectra of these van der Waals molecules. The ones that have been tested include the potential energy surfaces for the N2 dimer, [13][14][15][16]17'18 H,HF,19,[20][21][22][23][24] Recently, a new, physically motivated theoretical method of calculating IPS for van der Waals molecules has been developed. [25][26][27][28][29][30][31][32][33][34][35] This method, referred to as the many-body symmetry-adapted perturbation theory (SAPT), has been ap plied with success to determine interaction potentials for the HeF",(Ref.…”

The van der Waals rovibrational states of the Ar–NH3 dimer

“…A more detailed view of the potential surface at the equilibrium distance o R e = 3.59 A is given in Ref. 11. However, that view shows only the irreducible part of the potential surface 0°<(p<60°, whereas Fig.…”