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

The Journal of Chemical Physics

1991

Self Cite

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.

Section: Discussion Of the Potentialmentioning

confidence: 61%

Section: > (Degrees)mentioning

confidence: 99%

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

Bulski

Wormer

The Journal of Chemical Physics

1991

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“…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.…”

Section: Introductionmentioning

confidence: 99%

“…2/jlB" (22) Equation (22) gives (R) = 6.82 bohr, substantially larger than the equilibrium distance of the HeHF(i> = 0) potential Rm = 6.18 bohr.…”

mentioning

confidence: 99%

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

Moszyński

Jeziorski

The Journal of Chemical Physics

et al. 1994

Starting from an ab initio symmetry-adapted perturbation theory potential energy surface we have performed converged variational and close-coupling calculations of the bound rovibrational states and of the positions and widths of rotationally predissociating resonances of HeHF and HeDF van der Waals complexes. The energy levels were used to compute transition frequencies in the near-infrared spectra of these complexes corresponding to the simultaneous excitation of vibration and internal rotation in the HF(DF) subunit in the complex. The computed transition energies and other model independent characteristics of the near-infrared spectra are in excellent agreement with the results of high-resolution measurements of Lovejoy and Nesbitt [C. M. Lovejoy and D. J. Nesbitt, J. Chem. Phys. 93, 5387 (1990)]. In particular, the ab initio potential predicts dissociation energies of 7.38 and 7.50 cm " ' for HeHF and HeDF, respectively, in very good agreement with the Lovejoy and Nesbitt results of 7.35 and 7.52 cm -1. The agreement of the observed and calculated linewidths is less satisfactory. We have found, however, that the linewidths are very sensitive to the accuracy of the short-range contribution to the Vj(r,/?) term in the anisotropic expansion of the potential. By simple scaling of the latter component we have obtained linewidths in very good agreement with the experimental results. We have also found that this scaling introduces a very small (2%) change in the total potential around the van der Waals minimum.

“…The inversion-tunneling of NH3 was originally included by a simple two-state model, but presently we have extended our formalism and computer codes with a basis for the NH3 umbrella coordinate, so that we can include explicitly the U2 vibration and the inversion-tunneling of the NH3 monomer in the Ar-NH3 complex. The results are extensively described in recent papers by Van Bladel et al [86,87] and compared in detail with experimental d ata [78][79][80][81][82][83][84][85], Since the topic of Van der Waals molecules will be covered in this workshop by Hutson and by Brechignac, I have limited myself here to a summary of the main conclusions. It has been found that, indeed, the spectra of these Van der W aals complexes are extremely sensitive to the shape of the potential surface in the entire attractive region.…”

Section: Experim Ent Spherical Expansionmentioning

confidence: 99%

Overview on Intermolecular Potentials

Status and Future Developments in the Study of Transport Properties

1992

In trod u ctionAs will be substantiated in this workshop, the knowledge of intermolecular potentials opens the way to (the calculation of) many observable properties, for microscopic as well as macroscopic systems. In the first category are thermodynamic stability, the spectra of Van der Waals molecules [1][2][3][4], an d molecular beam scattering cross sections [5][6][7], elastic or inelastic state-to-state, to tal or differential. In the second category are various bulk gas and condensed m atter properties. Measured gas phase properties [8,9] which depend directly on the intermolecular potential are virial coef ficients, viscosity and diffusion coefficients, therm al conductivity, sound absorption, pressure broadening of spectral lines, nuclear m agnetic relaxation and depolarized Rayleigh scattering. Additional information is obtained from the effects of electric and magnetic fields on the transport properties (Senftleben-Beenakker effects). 2stability and lattice vibrations of molecular solids [11]. On the other hand, all the measured data may be used, and have actually been used in several examples, to construct or improve (semi-)empirical intermolecular potentials.Several reviews on intermolecular potentials have appeared during the past five years [2,3,[12][13][14][15][16], and hence I shall simply outline the most important points. In teractions between molecules are usually divided into long-range interactions and short-range interactions. At long range, i.e. when the charge clouds of the interacting molecules do not overlap, the interaction energy can be obtained formally by standard Rayleigh-Schrödinger perturbation theory. The perturbation, which is the intermolecular interaction operator, can be expanded as a multipole series in powers of R~1, where R is the distance between th e centers-of-mass of the molecules. The first-order energy is the electrostatic multipole-multipole interaction energy. The second-order energy contains the induction (multipole-induced multipole) energy and the (nonclassical) dispersion energy. For molecular ions the electrostatic and induction in teractions are strongly dominant. For polar, e.g. hydrogen bonded, molecules the electrostatic interactions are still the most important contribution, while the induc tion and dispersion energies are comparable. For apolar molecules, i.e. molecules with small dipole moments, the dispersion energy becomes the most important (attractive) long range interaction. The long range interactions are completely determined by the permanent multipole moments and the, static as well as frequency-dependent, multi pole polarizabilities of the monomers.Since the molecular charge clouds have exponential tails, there is always some overlap between them. The effects of this overlap are twofold. Penetration causes the exact electrostatic interaction between continuous, overlapping charge clouds to deviate from its representation by a multipole series. This is correctly included in the Rayleigh-Schrodinger perturbation theory if one avoids the expansi...