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

Abstract

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.