Dispersion Energy Constants Research Articles

Interferometric measurements of the dipole polarizability α of molecules between 300 K and 1100 K

A new interferometric method is used to determine the temperature dependence of the dispersion of the polarizability α of gaseous argon, hydrogen and oxygen, respectively. Although only the small wavelength range between 543·51 nm and 632·99 nm is covered, the data obtained in the temperature range 300 K < T < 1010 K are useful to derive important molecular properties like effective oscillator strengths and excitation energies, dispersion energy constants, and polarizability derivatives.

Pseudo-spectral dipole oscillator strengths and dipole-dipole and triple-dipole dispersion energy coefficients for HF, HCl, HBr, He, Ne, Ar, Kr and Xe

Pseudo-dipole oscillator strengths and excitation energies, which are discrete representations of original continuous dipole oscillator strength distributions (DOSDs), are tabulated for the ground state HF, HCl and HBr molecules and Ne, Ar, Kr and Xe atoms. These pseudo DOSDs are used to evaluate the dipole-dipole and triple-dipole dispersion energy constants for all possible two- and three-body interactions between HF, HCl, HBr, He, Ne, Ar, Kr and Xe. The importance of these results, and of the original DOSDs, is discussed briefly.

Pseudo-spectral dipole oscillator-strength distributions for SO2, CS2 and OCS and values of some related dipole—dipole and triple-dipole dispersion energy constants

Pseudo-spectral dipole oscillator strengths and excitation energies, which are discrete representations of the original continuous dipole oscillator-strength distributions (DOSDs), are presented for the ground-state SO2, CS2 and OCS molecules. These pseudo-DOSDs, together with previously published pseudo-DOSDs, are used to evaluate the dipole—dipole and triple-dipole dispersion-energy coefficients for all the two- and three-body interactions between SO2, CS2 and OCS and between these molecules and H2, N2, O2, NO, N2O, H2O, NH3, CO, CO2, CH4, C2H6, C4H10 and C6H14, with an estimated uncertainty of 1–2%. The importance of results of this type is discussed briefly.

On the additivity of atomic and molecular dipole properties and dispersion energies using H, N, O, H2, N2, O2, NO, N2O, NH3and H2O as models

The zeroth-order theory of intermolecular forces is used to derive additivity relations for rotationally averaged molecular dipole properties and dispersion energy constants by assuming that a molecule is comprised of non-interacting atoms or molecules. Some of the additivity rules are new and others, for example the mixture rule for dipole oscillator strength distributions (DOSDs), Bragg's rule for stopping cross sections and Landolt's rule for molecular refractivities, are well known. The additivity rules are tested by using previously constructed DOSDs and reliable values for the dipole oscillator strength sums Sk , Lk and Ik , and dispersion energy constants C 6, for H, N, O, H2, N2, O2, NO, N2O, NH3 and H2O as models. It is found that additivity is generally unreliable for estimating molecular properties corresponding to k < -2. Generally for k ≥ -2 and for C 6, and if the hydrogen molecule is used to represent the hydrogen atom in the additivity rules, the additivity relations yield results that are...

Pseudospectral dipole oscillator strength distributions and some related two body interaction coefficients for H, He, Li, N, O, H2, N2, O2, NO, N2O, H2O, NH3, and CH4

Pseudospectral dipole oscillator strength distributions (DOSDs) are presented for ground state Li, N, O, H2, N2, O2, NO, N2O, H2O, NH3, and CH4. The pseudo DOSDs are constructed by requiring the pseudodipole (excitation energy–oscillator strength) pairs to reproduce known values of the dipole oscillator strength sums S (k) evaluated from original DOSDs which are either completely continuous or contain a substantial continuum contribution. The pseudo DOSDs, which are a discrete representation of the original DOSDs, can be used to evaluate a variety of molecular properties in almost a trivial way, without sacrificing accuracy, by using discrete pseudospectral representations of the properties. The pseudostate DOSDs, together with ab initio pseudostates for the ground state H and He atoms, are used to evaluate orientation averaged dipole–dipole dispersion energy constants, C6(a,b), and the corresponding relativistic coefficients, W4(a,b), for all pairs of atoms and molecules taken form H, He, Li, N, O, H2, N2, O2, NO, N2O, H2O, NH3, and CH4. The results are used to assess the accuracy of semiempirical formulae for C6(a,a) and W4(a,a) and of combination rules for C6(a,b) and W4(a,b). The method of using pseudo DOSDs for the evaluation of molecular properties, relative to using the original DOSDs, becomes more important as the number of integrals over DOSDs in the definition of a property increases.

Re-evaluation of some lithium dipole properties and dipole-dipole and dipole-quadrupole van der Waals constants

Our previous one-centre pseudo-state results for some ground-state Li atom dipole oscillator strength sums, the dipole-dipole dispersion energy constants for the Li-Li, Li-H and Li-He ground-state interactions and the dipole-quadrupole dispersion energy constant for the Li-Li interaction are re-evaluated in the light of a more reliable selection for the resonance dipole oscillator strength of the Li atom. These and some of our previous lithium pseudo-state results are compared with corresponding literature values.

Dipole spectrum, sums and properties of ground-state methane and their relation to the molar refractivity and dispersion energy constant

Experimental and theoretical photo-absorption and high energy inelastic electron scattering cross sections, together with refractivity and sum rule constraints, are used to construct the non-relati...