Non-additive intermolecular forces from the spectroscopy of Van der Waals trimers: A comparison of Ar2–HF and Ar2–HCl, including H/D isotope effects

Abstract

Variational calculations of vibrational energies, rotational constants and angular expectation values are carried out for the trimers Ar 2 -HCl, Ar 2 -DCl, Ar 2 -HF and Ar 2 -DF. Calculations are performed on pairwise additive potential energy surfaces and on surfaces including a variety of non-additive contributions. Attention is focused on the bending levels corresponding to hindered internal rotation of the HX molecule in the complex, several of which have been observed by high-resolution spectroscopy. The results confirm that it is crucial to include dispersion, induction and short-range effects when modelling the non-additive forces in molecular systems. It is found that the model of non-additive forces previously proposed by Ernesti and Hutson ͓Phys. Rev. A 51, 239 ͑1995͔͒ works well for the bending bands of Ar 2 -HCl, Ar 2 -DCl and Ar 2 -DF as well as Ar 2 -HF. In addition, a new distributed model of the non-additive dispersion energy is proposed, in which the triple-dipole energy is partitioned between two anisotropic sites in the HX molecule.

Clusters containing open-shell molecules. II. Equilibrium structures of ArnOH Van der Waals clusters (X2Π, n=1 to 15)

“…Accordingly, the trimer spectra were used to develop models for the nonadditivity. 15,16 It was found that novel nonadditive terms, arising from the interaction of the HF permanent multipole moments with overlapinduced multipoles on the Ar atoms, were needed to describe the spectra.…”

“…Electronic mail: zlatko.bacic@nyu.edu b͒ Electronic mail: j.m.hutson@durham.ac.uk tial energy surfaces, have been extended to the low-lying isomers of Ar n HF clusters with nр7 and nϭ12. 23 In a recent development, the work on nonadditive forces 15,16 and on cluster structure and dynamics 18 -22 has been brought together, and the nonadditive models developed for Ar 2 HF have been applied to larger Ar n HF clusters. 24 The nonadditive potentials were found to account remarkably well for the frequency shifts for nϭ3 and n ϭ4, 24 which were the largest Ar n HF clusters that had then been observed.…”

Calculating energy levels of isomerizing tetra-atomic molecules. I. The rovibrational bound states of Ar2HF

“…Investigations of the nonadditive forces in the Ar 2 HF complex using ab initio electronic structure calculations have included the applications of supermolecular Møller-Plesset perturbation theory by Szczȩśniak, Chała-sinski, and co-workers 10,11 and symmetry-adapted perturbation theory by Moszynski and co-workers. 16 Hutson and co-workers 2,12,14,[21][22][23] have developed and tested a model of the nonadditive forces in Ar 2 HX ͑where X ϭ halogen͒ including dispersion, induction, exchange overlap and exchange multipole interactions. Ernesti and Hutson 14 found that their total-1 model ͑referred to hereafter as the EH potential͒ reproduced well the vibrational band origins and frequency shifts for Ar 2 HF, Ar 2 DF, Ar 2 HCl, and Ar 2 DCl in the H/DX vϭ0 and 1 states.…”

“…16 Hutson and co-workers 2,12,14,[21][22][23] have developed and tested a model of the nonadditive forces in Ar 2 HX ͑where X ϭ halogen͒ including dispersion, induction, exchange overlap and exchange multipole interactions. Ernesti and Hutson 14 found that their total-1 model ͑referred to hereafter as the EH potential͒ reproduced well the vibrational band origins and frequency shifts for Ar 2 HF, Ar 2 DF, Ar 2 HCl, and Ar 2 DCl in the H/DX vϭ0 and 1 states. The model has also been extended to Ar n HF clusters 24 and shown to reproduce the observed vibrational shifts for nϭ3 and 4.…”

“…Successful solution of this bound-state problem is vital to maximize the understanding of the spectroscopy of this important prototype system for the development of the theory of nonadditive ͑three-body͒ intermolecular forces. [9][10][11][12][13][14][15][16] The Ar 2 HF complex is ideally suited for the investigation of nonadditive forces in systems involving a molecular constituent. The Ar 2 and ArHF pair potentials are very accurately known, having been determined by accurate fitting to experimental data by Aziz 17 and Hutson, 18 respectively.…”