Measurement of the Spin-Orbit Perturbation in theP-State Continuum of Heavy Alkali-Metal Atoms: K, Rb, and Cs

Abstract

The spin-orbit interaction for the $P$-state continuum of heavy alkali metals was investigated in a photoionization experiment using spin-polarized alkali atoms and circularly polarized light. From the asymmetry in ion-counting rates corresponding to the two photon helicities, Fano's spin-orbit perturbation parameter $x$ was determined over a range of several hundred angstroms for K, Rb, and Cs. The spin-orbit perturbation was found to increase from K to Rb to Cs as expected, and the nonlinear behavior of $x$ as a function of the photon energy $E$ was demonstrated for K. Knowledge of $x\left(E\right)\mathrm{}$ was used to establish accurate values for the position of the Cooper minimum and to estimate the magnitude of the cross section at the minimum. In addition, the $x\left(E\right)\mathrm{}$ data for Cs were used to gain information about the spin polarization of photoelectrons in a Fano-type polarized electron source. Finally, extrapolation of $x\left(E\right)\mathrm{}$ for cesium into the discrete spectrum indicated the existence of a pole in the function $\rho \mathrm{}\left(E\right)\mathrm{}$ which corresponds to the doublet line-strength ratio $\rho \left(E_{\mathrm{nP}}\right)=\frac{S\left(n{P}_{\frac{3}{2}}\right)}{S\left(n{P}_{\frac{1}{2}}\right)}$ at the discrete energies $E_{\mathrm{nP}}$. According to our extrapolation, the pole lies in the region of $n=10\mathrm{} \mathrm{to} 15$, in agreement with the early spectroscopic work of Sambursky (1928) and Beutell (1939), whose measurements were discounted by later investigators.