Positron-induced scattering from pentane isomers beyond ionization threshold

The binary encounter Bethe model (BEB) for positron is invoked to obtain the positron impact direct ionization cross sections for pentane isomers from ionization threshold to 5000 eV. The BEB results are compared with the theoretical results, and the agreement is found to be good. The elastic cross sections (ECS) are obtained using the single-center expansion (SCE) approach. The incoherently summed elastic and direct ionization cross sections are in an excellent agreement with the experimentally measured total cross sections (TCS) from 40 eV onwards. The cross sections for a particular type of a process were similar for all the isomers, thus indicating absence of isomerism in positron impact scattering. The differences in the magnitude of the differential cross sections (DCS) of the three isomers were small. But the isomer effect could be assessed by the contribution of different partial waves in the DCS, where for neo-pentane the oscillatory pattern differs from the n-pentane and iso-pentane. We have also compared the electron and positron BEB ionization cross sections. Beyond 500 eV, cross sections from both the projectiles show merging trends.