Determinação das seções de choque elásticas para colisões de pósitrons com as moléculas F2 e Cl2

Abstract

This work presents differential and integral cross sections for the elastic scattering of positron with molecules F2 and Cl2 at low energy, between 1 and 20 eV. A scattering potential model was employed within the static-correlation-polarization approximation, involving terms of dipolar and quadrupolar polarization, the first and second hyperpolarizabilities, the correlation potential between positrons and molecules, as well as the electrostatic potential. In this perspective, the Method of Continued Fractions was used, along with the potential model, to solve the scattering equations. This method proved to be efficient in calculating cross sections for positrons collisions with other molecules, both in computational applicability and accuracy of results, as we can verify in the case of O2. Similarly, a systematic study of the description of polarization levels was conducted by including term-by-term interaction of higher-orders polarization in the scattering potential and the effects of this insertion produces on the cross sections and phase shifts of the respective target molecules of this research. Furthermore, interesting phenomena related to positrons scattering with molecules have been observed in the low-energy region, namely, the Ramsauer-Townsend effect. Likewise, comparisons of our phase shifts calculations with the results available in the literature for Cl2 are performed. The present results demonstrate the existence of a bound state. In this way, our results contribute significantly to a deeper understanding of the scattering dynamics of positron with the molecules studied is this work.