A reliable new three-dimensional potential energy surface for H2–Kr

Abstract

An improved three-dimensional potential energy surface for the H(2)-Kr system is determined from a direct fit of new infrared spectroscopic data for H(2)-Kr and D(2)-Kr to a potential energy function form based on the exchange-Coulomb model for the intermolecular interaction energy. These fits require repetitive, highly accurate simulations of the observed spectra, and both the strength of the potential energy anisotropy and the accuracy of the new data make the "secular equation perturbation theory" method used in previous analyses of H(2)-(rare gas) spectra inadequate for the present work. To address this problem, an extended version of the "iterative secular equation" method was developed which implements direct Hellmann-Feynman theorem calculation of the partial derivatives of eigenvalues with respect to parameters of the Hamiltonian which are required for the fits.

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

“…Although the adjustable parameters for the final, XC͑fit͒, potential energy surfaces ͑PESs͒ constructed for the H 2 -Ar, Kr interactions 7,8 were determined primarily on the basis of fits to accurate spectroscopic data, these potential surfaces have also been shown to give excellent agreement with experimental data for phenomena that were not utilized in the fitting procedure. For the H 2 -Ar interaction, calculated and measured inelastic differential scattering data, hyperfine transition frequencies, 7 and, to a more limited extent, gas phase nuclear magnetic relaxation times 16 have been compared, while for the H 2 -Kr interaction, comparison has been made between calculated and measured temperature dependences of the interaction second virial and binary diffusion coefficients.…”

“…Moreover, for those cases in which the diatom bond length r is not held fixed, in practice it is often replaced 7,8 by the dimensionless stretching coordinate ϵ͑r − r 0 ͒ / r 0 defined in terms of a fixed reference distance r 0 . For a molecule in its ground vibrational state, for example, a reasonable choice for r 0 is the expectation value of r, which for CO has the value 39 r 0 ϵ r 0 ͑CO͒ = 2.139 93a 0 .…”

“…For the H 2 -Ar interaction, calculated and measured inelastic differential scattering data, hyperfine transition frequencies, 7 and, to a more limited extent, gas phase nuclear magnetic relaxation times 16 have been compared, while for the H 2 -Kr interaction, comparison has been made between calculated and measured temperature dependences of the interaction second virial and binary diffusion coefficients. 8 In all cases, the XC͑fit͒ PESs have fared well.…”

“…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.…”

“…Given the accuracy with which PESs representing interactions between Rg atoms and H 2 and N 2 molecules [7][8][9][10][11][12][13] and between He and the CO molecule 14,20 can be constructed, as shown by the ability of such PESs to predict MW and IR spectra of Rg-N 2 and He-CO van der Waals dimers and bulk properties of Rg-N 2 and He-CO binary mixtures, it is worthwhile to apply the XC model to the description of other Rg-CO interaction energies. The purpose of the present paper is to examine the simplest such Rg-CO interaction, namely, the Ne-CO interaction, as the Ne-CO van der Waals dimer has recently been the subject of a number of spectroscopic investigations, including MW, 24 millimeter-wave [25][26][27] ͑MMW͒, and midinfrared 28,29 ͑mid-IR͒ measurements.…”