Relativistic many-body calculation of energies, lifetimes, hyperfine constants, and polarizabilities inL7i

Abstract

The excitation energies of $ns$, $np$, $nd$, and $nf$ $(n\ensuremath{\le}6)$ states in neutral lithium are evaluated within the framework of relativistic many-body theory. First-, second-, third-, and all-order Coulomb energies and first- and second-order Breit corrections to energies are calculated. All-order calculations of reduced matrix elements, oscillator strengths, transition rates, and lifetimes are given for levels up to $n=4$. Electric-dipole $(2s\ensuremath{-}np)$, electric-quadrupole $(2s\ensuremath{-}nd)$, and electric-octupole $(2s\ensuremath{-}nf)$, matrix elements are evaluated to obtain the corresponding ground-state multipole polarizabilities using the sum-over-states approach. Scalar and tensor polarizabilities for the $2{p}_{1/2}$ and $2{p}_{3/2}$ states are also calculated. Magnetic-dipole hyperfine constants $A$ are determined for low-lying levels up to $n=4$. The quadratic Stark shift for the $(F=2\text{ }M=0)\ensuremath{\leftrightarrow}(F=1\text{ }M=0)$ ground-state hyperfine transition is found to be $\ensuremath{-}0.0582\text{ }\text{Hz}/{(\text{kV}/\text{cm})}^{2}$, in slight disagreement with the experimental value $\ensuremath{-}0.061\ifmmode\pm\else\textpm\fi{}0.002\text{ }\text{Hz}/{(\text{kV}/\text{cm})}^{2}$. Matrix elements used in evaluating polarizabilities, hyperfine constants, and the quadratic Stark shift are obtained using the all-order method.