Relativistic R -matrix calculations for the electron-impact excitation of neutral molybdenum

Abstract

A recent PISCES-B Mod experiment [Nishijima et al., J. Phys. B 43, 225701 (2010)] has revealed up to a factor of 5 discrepancy between measurement and the two existing theoretical models [Badnell et al., J. Phys. B 29, 3683 (1996); Bartschat et al., J. Phys. B 35, 2899 (2002)], providing important diagnostics for Mo i. In the following paper we address this issue by employing a relativistic atomic structure and $R$-matrix scattering calculations to improve upon the available models for future applications and benchmark results against a recent Compact Toroidal Hybrid experiment [Hartwell et al., Fusion Sci. Technol. 72, 76 (2017)]. We determine the atomic structure of Mo i using grasp${}^{0}$, which implements the multiconfigurational Dirac-Fock method. Fine structure energies and radiative transition rates are presented and compared to existing experimental and theoretical values. The electron-impact excitation of Mo i is investigated using the relativistic $R$-matrix method and the parallel versions of the Dirac atomic $R$-matrix codes. Electron-impact excitation cross sections are presented and compared to the few available theoretical cross sections. Throughout, our emphasis is on improving the results for the $z\phantom{\rule{0.16em}{0ex}}^{5}P_{1,2,3}^{o}\ensuremath{\rightarrow}a\phantom{\rule{0.16em}{0ex}}^{5}S_{2},\phantom{\rule{0.16em}{0ex}}z\phantom{\rule{0.16em}{0ex}}^{7}P_{2,3,4}^{o}\ensuremath{\rightarrow}a\phantom{\rule{0.16em}{0ex}}^{7}S_{3}$ and $y\phantom{\rule{0.16em}{0ex}}^{7}P_{2,3,4}^{o}\ensuremath{\rightarrow}a\phantom{\rule{0.16em}{0ex}}^{7}S_{3}$ electric dipole transitions of particular relevance for diagnostic work.