Measurements of spin-orbit perturbation in atomic rubidium through photoelectron angular distributions.

Abstract

We discuss measurements of the angular distributions of photoelectrons produced by photoionizing ground-state rubidium with light of wavelengths between 266 and 285.3 nm. The spin-oribit perturbation in this heavy element affects the ratio of the oscillator strength for excitation to the ${\mathit{P}}_{3/2}$ state to that for excitation to the ${\mathit{P}}_{1/2}$ state. For our measurements the electron energy approaches that of the Cooper minimum in the photoionization spectrum, the effect of which is to reduce the asymmetry parameter from the nonrelativistic value of 2. At the shortest wavelength for which we have measured these distributions, the cross section for ionization to the \ensuremath{\epsilon}${\mathit{P}}_{1/2}$ state has nearly vanished.