Semiempirical models for low energy positron scattering by Ar, Kr and Xe

Abstract

Positron scattering by Ar, Kr and Xe was investigated considering two well-established semiempirical potentials with different descriptions of the asymptotic positron–atom scattering potential. Exploring the ultimate nature of semiempirical formulations, two independent semiempirical models were studied. In the first model, the potential parameters were fixed to reproduce the experimental values of the positron–atom scattering length, while, in the second, they were tuned to better fit experimental absolute folded differential cross sections through a χ2 approach. Results showed that the introduction of higher order polarisabilities and hyperpolarisabilities considerably improved the description of the forward scattering and the total and grand-total experimental low energy cross sections.

Semiempirical Calculations on Low-Energy Electron Scattering by Zn and Cd Atoms

“…Following our previous works [16,18] and particularly inspired by the article of O'Connel and Lane [19], we write the effective Hamiltonian for the electron-atom system as…”

“…In our previous investigations on positron-atom scattering [15,16,18], we adopted the model electronic density of Salvat et al [25]. As highlighted by Rabasović et al [26], the model densities given by Salvat et al [25] provide a poor representation of the atomic shell structure.…”

“…Opposed to ab initio and model potential formulations, semiempirical approaches are based on adjustable parameters, usually tuned to reproduce some external previously known quantity. In practice, we are going to work with a single-body potential to represent the electron-atom interaction whose polarization component has asymptotically correct form up to the first order [16,17], and its short range component is adjusted to reproduce the position of the p-wave resonances at the energies observed by Burrow et al [4].…”

The Hidden Ramsauer-Townsend Effect in Positron Scattering by Rare Gas Atoms

“…Later, Ivanov and Mitroy [17] improved it using a cutoff function that makes a smooth connection between the short static and long range polarization potentials. Recently, Arretche et al [18] studied the influence of atomic hyperpolarizabilities and compared the efficiency of well-established semiempirical potentials to represent the modern experimental data for total and differential cross sections for Ar, Kr, and Xe. Inspired in the results obtained in this investigation, we consider here a semiempirical polarization potential of the form:…”

“…The spirit of the semiempirical method is to adjust the cutoff parameter r c to reproduce some external data previously known from experiment or theory like binding energies, scattering lengths, or sophisticated ab initio calculations. For Ar and Xe, we follow the work of Arretche et al [18], where the cutoff parameters were fixed in order to reproduce the scattering lengths measured by Zecca et al [19,20]. For Ne, we have considered the scattering length equal to 1.650 a 0 because it better fits the energy position of the RT observed in the experimental TCS.…”