Elastic scattering of electrons by strontium and barium atoms

Differential, total, and momentum transfer cross sections for the elastic scattering of low- and intermediate-energy (0.2--100 eV) electrons by Sr and Ba atoms were calculated in the relativistic polarized orbital approximation. A static part of the projectile-target interaction potential was generated by solving the Dirac-Hartree-Fock (DHF) equations for the isolated target. A polarization potential was obtained by solving the coupled DHF equations for the target perturbed by an electric field produced by the projectile. Only the dipole term in the polarization potential was included in scattering calculations. For low angular momenta (0[le][ital l][le]5) relativistic phase shifts were extracted by solving a continuum state DHF equation in an inner region, where exchange between the projectile and the target electrons was important, and then a relativistic variable phase (RVP) equation in an outer region, where exchange was negligible. For intermediate angular momenta (6[le][ital l][le]17) exchange was neglected and the phase shifts were calculated by solving the RVP equation in the whole configuration space. Higher ([ital l][ge]18) phase shifts were obtained using the Born approximation and their contributions to scattering amplitudes and cross sections were evaluated analytically. At low energies (0.2--10 eV) our total cross sections for both Sr and Ba atoms differ seriously from experimental data of Romanyuk, Shpenik, and Zapesochnyi (Pis'ma Zh. Eksp. Teor. Fiz. 32, 472 (1980) [JETP Lett. 32, 452 (1980)]). At energies up to 60 eV our differential cross section for Ba differs both in magnitude and shape from experimental data of Jensen, Register, and Trajmar [J. Phys. B 11, 2367 (1968)] but quite satisfactorily reproduces shapes of curves measured recently by Wang, Trajmar, and Zetner [J. Phys. B (to be published)]. At energies above 80 eV the agreement between the present results and the data of Jensen, Register, and Trajmar is much more satisfactory.