Positron scattering from molecular hydrogen

Abstract

We present results for total and partial cross sections for positron scattering from H 2 . The total scattering and positronium formation cross sections are reported between 0.5 and 200 eV. Total quasielastic and inelastic scattering cross sections are reported for energies between the positronium formation threshold and 50 eV, with quasielastic differential scattering cross sections reported at 1, 3, 5, 7, and 10 eV. Our results are compared with previous work, both experimental and theoretical, with particular attention paid to the region below the positronium formation threshold, where there are apparent discrepancies in previous work. A discussion of possible reasons for discrepancies between this and previous work is presented, including a focus on known systematic effects in the experimental results.

Model-potential calculations of positron binding, scattering, and annihilation for atoms and small molecules using a Gaussian basis

“…This is clear evidence of the ability of the present method to accurately describe lowenergy scattering of positrons by small molecules. Finally, the figure shows the phase shift of Fedus et al [110], which was determined empirically by performing a fit based on modified effective-range theory to experimental data of Machacek et al [111] on the e + -H 2 elastic scattering cross section. The result of this fit is very close to the present calculation for positron momenta k 0.1 a.u., but lies slightly higher at larger k. −2.39 a.u., respectively.…”

Low energy positron interactions with uracil—Total scattering, positronium formation, and differential elastic scattering cross sections

“…In this context the measurements are "quasi-elastic" as we cannot resolve rotational and some vibrational contributions from the purely elastic scattering with the present energy resolution (this has been discussed in detail previously 6,8,28 ). Tabulated values of these as-measured cross sections, together with values which have been adjusted with the IAM normalization factor of 2.21, are given in Table IV, these scaled values is that any uncertainty in the gas number density determination, as speculated above, will also affect the magnitude of the measured differential cross sections, but not the angular distribution.…”

A rigid sphere approach to positron elastic scattering by noble gases, molecular hydrogen, nitrogen and methane

“…Figure 7a shows present calculations of elastic crosssections for molecular hydrogen (H 2 ) using three different values of rigid sphere radius: R 0 = 0.9221a 0 , R 0 = 0.9509a 0 and R 0 = 0.9912a 0 . Present results are compared with three the most recent experimental TCSs [51,73,74] and selectively chosen recent theoretical data. Calculations with the smallest R 0 yield elastic cross-sections, which agree pretty well with experimental TCS measured by ANU group [74].…”

“…Present results are compared with three the most recent experimental TCSs [51,73,74] and selectively chosen recent theoretical data. Calculations with the smallest R 0 yield elastic cross-sections, which agree pretty well with experimental TCS measured by ANU group [74]. The agreement is particularly good above 2 eV, at the "flat" part of cross-sections, just below positronium formation threshold.…”

“…To best [65], Zammit et al [66] and Fedus et al [3]; theories for N2: Elza et al [67], Carvalho et al [68], Tenfen et al [69], Mukherjee and Mukherjee [70] and Franz et al [10]; theories for CH4: Jain and Gianturco [71], Zecca et al [72] and Franz et al [10]. Experiments for H2: Fedus et al [3], Karwasz et al [51], Zecca et al [73] and Machacek et al [74]; experiments for N2: Hoffman et al [75], Sueoka and Hamada [76], Karwasz et al [51] and Zecca et al [77]; experiments for CH4: Floeder et al [78], Sueoka and Mori [79], Dababneh et al [80] and Zecca et al [72].…”