B-Spline R-Matrix with Pseudo-States Treatment of Electron Collisions with Argon

We have further developed the $B$-Spline $R$-matrix (BSR) code~[1] to allow for a large number of pseudo-states in the close-coupling expansion. In the present work, the BSRMPS approach~[2] was employed to perform semi-relativistic (Breit-Pauli) close-coupling calculations for elastic scattering, excitation, and ionization of argon from both the ground state and the metastable excited states. Coupling to the ionization continuum through the pseudo-states is important for low-energy elastic scattering (to represent polarizability effects), for excitation in the ``intermediate'' energy regime of about 1-3 times the ionization potential, and to allow for the calculation of ionization processes by transforming the results obtained for excitation of the positive-energy pseudo-states. The current results represent a significant extension of our earlier near-threshold work~[3].\\[4pt] [1] O.~Zatsarinny, Comp. Phys. Commun.~{\bf 174} (2006) 273.\\[0pt] [2] O.~Zatsarinny and K.~Bartschat, Phys.~Rev.~Lett.~{\bf 107} (2011) 023203.\\[0pt] [3] O.~Zatsarinny and K.~Bartschat, J.~Phys.~B~{\bf 37} (2004) 4693.