lide Positron - methyl halides scattering dynamics

Nidhi  Sinha, Paresh Modak, Suvam Singh and Bobby Antony   
Atomic and Molecular Physics Lab,  Department of Applied Physics, Indian Institute of Technology (Indian school of  Mines), Dhanbad-826004, Jharkhand, India  

Abstract

The well known Spherical Complex Optical Potential (SCOP) and Complex Spherical Potential-ionisation contribution (CSP-ic) method with proper modification is applied to the CH3X (X=Cl, Br and I) molecules to compute the positron impact scattering cross sections, which rather is a first theoretical attempt to report the same. Besides, the various inelastic cross sections for the present targets is new in literature. In general, a reasonable accordance has been found between the present total cross sections and the experimental measurements. However, the observed inconsistency between the theoretical values and experimental cross sections in the low energy region persist in this work. Furthermore, based on the present data set, we have attempted to propose a semi-empirical formula for \(Q_{tot}\), depending on the target parameters which would be useful to determine the total cross sections in the high energy region. \(\sigma\)

Introduction

Recent decades have witnessed augmented focus on positron scattering from various targets. This rest on the vast contribution of such phenomenon in different fields. Guided by these applications, our group have extended the research focus on positron-target collisions. The present work is an addition to this endeavor.  We have chosen the less attended methyl halide group as targets in this article. These molecules yield majority of the inorganic free halogen radicals to the stratosphere resulting in ozone depletion. Also CH3F find vital applications in biochemistry and mass spectroscopy. Furthermore, methyl bromide and methyl iodide are potential candidates as soil fumigant. The cross sectional data for these targets are used in analysis of various phenomena. The cross sections for positron-molecule interactions help us give a better insight of the particle track simulations. Modelling software such as GEANT, PENELOPE and LEPTS use these cross sections as their basic input to estimate radiation induce damage. 
\(sigma\ b\)
The only available previous data is the experimental measurements of  Kimura et al. \cite{Kimura_2001}; however, no such theoretical effort has been made. The present computed cross sections are thus the first theoretical report for the present targets. Furthermore, the various inelastic cross sections are reported for the first time.