20 September 1999 Ž . Physics Letters A 260 1999 360–364 www.elsevier.nlrlocaterphysleta Modified semiclassical exchange approximation in electron–atom ž / collision He e, 2e triple differential cross-section Y. Khajuria, D.N. Tripathi ) Department of Physics, Banaras Hindu UniÕersity, Varanasi 221005, India Received 1 March 1999; received in revised form 14 July 1999; accepted 16 July 1999 Communicated by B. Fricke Abstract Ž . Ž . A modified semiclassical exchange MSCE potential has been used in the distorted wave born approximation DWBA Ž . Ž 2 . to calculate the triple differential cross-section TDCS for He 1s at 64.6 and 74.6 eV incident electron energies in non-coplanar symmetric geometry. The agreements of present results with experimental data are much better as compared with our earlier calculations based on the spin averaged static exchange potential. q 1999 Elsevier Science B.V. All rights reserved. PACS: 34.80.Gs; 34.80.Dp Keywords: Triple differential cross-section; DWBA; Non-coplanar symmetric kinematics wx It has been reported 1 that local approximations for the exchange interaction between bound and continuum electrons affect the total cross-section appreciably at low collision energies in case of poly- atomic molecules. It is also well known that it is responsible for the observed Ramsauer–Townsend Ž . RT minima appearing in the integral elastic cross- wx section. In recently 2 reported results of the DWBA Ž . calculation of e, 2e triple differential cross-sections Ž 2 . for He 1s at 64.6 eV in different kinematical ge- ometries with the spin averaged static exchange in- wx teraction potential 3 , in which the polarization has been accounted implicitly although a qualitative agreement with the measurements of Read and Mur- ) Corresponding author. Fax: q91-542-317074; e-mail: dnt@banaras.ernet.in wx ray 4 is there, we found some noticeable differ- ences even after taking maximum possible care to ensure the convergence in the calculated cross-sec- tions. These obvious discrepancies are attributed mainly to the inefficacy of the static exchange inter- action potential that has been used. In particular, the exchange and the polarization terms which have significant contributions, have not been taken into wx account properly. Whelan et al. 5 included the post collision interaction through Gammow factor and also the polarization in their distorted wave approach to improve agreements of their results with the ex- periment. The post collision interaction has been shown to be prominent only for 08 incident electron wx angle 6 . It is natural therefore, to infer that the interaction potentials used so far are deficient in describing the Ž . observed e, 2e TDCS for He atom particularly, in the low energy region. In this note modified semi- 0375-9601r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved. Ž . PII: S0375-9601 99 00486-7