Argon dimer potentials

Fig. 20.5. Calculated bond energy potentials of argon dimer for long-range exchange corrected functionals (LC-SOP, LC-BOP, and LC-PBEOP). Pure functionals are also presented for comparison. Highly accurate potentials are also shown for comparison.

The intermolecular potential curves for rare gas atoms have been extensively studied. The potential curve for argon dimer is shown in Fig. 1. The way in which it has been determined is discussed elsewhere.The left portion of the figure gives the potential... 

Fig. 3 Dissociation potential energy curves of argon dimer calculated with (a) various pure and long-range corrected (LC) functionals and (b) LC functionals combined with ALL dispersion functional. The curves of CCSD(T) and other dispersion-corrected DPT are also shown for comparison...

A very interesting field of research covers the spectroscopy of van der Waals molecules in search of more detailed information about the long range potential and the polarizability. Raman spectra of van der Waals dimers in argon have been observed and a vibrational frequency shift for I2-molecules from 213 cm" to 197 cm has been measured for I2 -Ar-complexes. 

L opez Cacheiro J, Fernandez B, Marchesan D, Coriani S, Hattig C, Rizzo A (2004) Coupled cluster calculations of the ground state potential and interaction induced electric properties of the mixed dimers of helium, neon and argon. Mol Phys 102 101-110... 

Recently, considerable effort has been devoted to obtaining quantum mechanical intermolecular potentials suitable for fluid simulations. For some examples see 75 for (HF)2 76 for (N2)2 77-80 for (CO)2 81 for the benzene dimer 82 for the SiH4 dimer 83 for water-argon and water-methane potentials 84 for the formamide dimer and N,N-dimethylformamide 85 for lithium iodide in dimethylsulfoxide and 86 for Ni2+ in aqueous solution. Rather than discuss each of these studies, here we will focus on a few important developments that we anticipate could alter the capacity or approach to development... 

Theoretical expressions for the reduced viscosity and thermal conductivity second virial coefficients are presented in Section 5.3. An important contribution arises from the effect of the formation of dimers, even though the concentration of dimers is still small. For the evaluation of these transport property virial coefficients it was assumed that both the interaction potential between two monomers and between a monomer and a dimer is of the Lennard-Jones (12-6) form but with different potential parameters. The ratios of these parameters, which are characterized by the constants 8 and 6 defined in Section 5.3, are determined from a large selection of experimental data. According to Stogryn Hirschfelder (1959), the mole fraction of dimers in argon is 0.2% at 0.1 MPa and 200 K, while this fraction reduces to 0.04% when the temperature rises to 600 K. 

The shape of the potential surface can be used to determine energy levels and partition functions and consequently the equilibrium constant for van der Waals molecule formation. This is done elsewhere.A typical result is that gaseous argon cooled to near its normal boiling point, where kT = De, contains a few percent of the dimer Ar2- Samples of similarly cooled nitrogen, oxygen, or hydrogen contain comparable concentrations of (N2)2j ( 2)29 r (H2)2-The use of supersonic nozzles produces beams characterized by temperatures often less than 10 K. Under these conditions the beam composition will be dominated by van der Waals molecules. 

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