General correlations between van der Waals interaction potential parameters and polarizabilities of the interacting neutral–neutral partners of any nature are presented and discussed. To ensure the full applicability of the correlations, an evaluation of the long-range interaction constants is performed in terms of the Slater–Kirkwood approximation whose numerical coefficients, having the meaning of effective electron numbers, are estimated interpolating the values deduced by theoretical considerations. The values of the long-range constants so obtained are compared satisfactorily with the available experimental ones. The correlations are tested successfully over practically all systems characterized experimentally. Their use to predict the parameters of unknown systems is suggested.
Many-body Green’s-function calculations which employ large configurational expansions and which are accurate to third and fourth order of perturbation theory are reported for the valence ionic states of HCl. Large polarized basis sets including Rydberg functions s-, p-, and d-type symmetries have been used. Third-order calculations are sufficient in the outer valence region, but in the inner valence region where the complete breakdown of the one-particle picture of ionization is observed a fourth-order theory is necessary in conjunction with large basis sets. The synchrotron and x-ray excited spectra can be assigned nearly up to the double-ionization threshold in a very satisfactory way. No indication of strong outer valence satellite lines is found.
The ionization of HC1 molecules by thermal energy collisions with metastable Ne* atoms has been studied experimentally and theoretically. The integral elastic cross sections have been measured and analyzed, together with the total ionization cross sections, to obtain an optical potential able to describe the collision dynamics of the neutral reactants. The relative cross sections for NeH+ and NeD+ production in Ne*-HCl or DC1 have been measured as a function of the collision energy. A theoretical calculation of the potential energy for the reactive N e + HCl+(A) -NeH+ + C1 system has been performed by SCF, CI, and CASSCF methods. The dynamics of NeH+ production is described by two theoretical models. The first onesimply couples the semiclassical treatment of Penning ionization with the Langevin criterion for the postionization ion-molecule reaction. The second model also assumes the statistical phase space theory to describe the partitioning of the Ne..-HCl+(A) ionic complex among the possible final products.
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