Improved modelling of atom–molecule potential-energy surfaces: illustrative application to He–CO

Abstract

The need for better potential-energy models for atom-molecule and molecule-molecule interactions is discussed and the utility of the exchangecoulomb (XC) model is critically examined, by fitting a potential based on it to new high-resolution discrete infrared data for the He-CO Van der Waals molecule. In addition to explaining the observed spectrum as well as does an optimized empirical potential previously determined from the same data, the resulting XC surface is expected to be more realistic in regions not directly sampled by the fitted data.

State to state Ne–CO rotationally inelastic scattering

“…This comparison suggests that while its repulsive wall is more accurate than the SAPT one, neither of the two surfaces is as accurate as the best He-CO surfaces. 41,42 Since we are attempting to judge the accuracy of the two surfaces by measuring the phase of the interference in the rotational excitation cross sections, it is important to determine whether both surfaces are on the same ''interference fringe.'' That is, if the propensity changes from even to odd ⌬ j many times as a model surface changes continuously from the SAPT to the CCSD͑T͒ surface, then the improved agreement of the latter with our observations might be accidental.…”

Potential generation and path‐integral Monte Carlo in study of microscopic superfluidity

“…Indeed, quantum Monte Carlo simulations of doped helium clusters are known to be very sensitive to the quality of the pair potentials, and most of the current discrepancies between theory and experiment can be traced back to the accuracy of the potentials. [13,14] Intermolecular potential energy surface (PES) can be determined from ab initio calculations, or least-squares fits to highresolution spectroscopic data [15][16][17][18][19] and molecular beam scattering experimental results. [20] Due to the limited availability of experimental data, the former approach is most popular.…”

“…A couple of years subsequent to these observations, a similar superfluid phenomenon was observed, this time involving para-H 2 (pH 2 ) clusters doped with an OCS chromophore and embedded in Helium nanodroplets. [9] For OCS(pH 2 ) 14,15,16 , as T drops from 0.38 to 0.15 K, the Q-branches of their rovibrational spectra disappear, indicating null rotational inertia along the OCS axis. This suggests a superfluid fraction of 100% of the pH 2 's around the axis.…”

An exchange-Coulomb model potential energy surface for the Ne–CO interaction. I. Calculation of Ne–CO van der Waals spectra

“…The only case for which an XC͑fit͒ PES has been determined for the interaction between a closed-shell atom and a closed-shell heteronuclear diatomic molecule is that of He with CO. 14 The He-CO van der Waals complex, unlike the He-N 2 complex, possesses a well-defined and relatively simple IR spectrum at low temperatures, so that the van der Waals dimer spectrum could be employed, together with the temperature dependence of the interaction second virial coefficient, to determine appropriate values for the fitting parameters. The He-CO XC͑fit͒ PES not only provides an excellent fit to the positions of the IR spectral lines of the He-CO dimer but also predicts the various transport properties of He-CO bulk gas mixtures better than other available high-quality PESs, such as the V ͑3,3,3͒ PES of Chuaqui et al 17 and the symmetry-adapted perturbation theory ͑SAPT͒ PESs of Moszynski et al 18 and Heijmen et al 19 ͑see Refs.…”

“…1-6 and references therein͒, the exchange-Coulomb ͑XC͒ model has been extended to provide accurate representations of the interaction energies between rare-gas ͑Rg͒ ͑He, Ne, Ar, Kr͒ atoms and homonuclear ͑H 2 , N 2 ͒ diatomic molecules [7][8][9][10][11][12][13] and between He and CO. 14 The current XC model for the dimer interaction energy employs Heitler-London first-order interaction energies to describe the predominantly repulsive short-range behavior and individually damped and overall-corrected dispersion energies to describe the predominantly attractive long-range behavior ͑see Ref. 15 and, for example, Ref.…”