First Experimental Determinations andR-Matrix Calculations of the Angular Distribution of Photoelectrons Ejected in Direct Inner-Shell Photoionization of Excited Atoms

Measurements of the angular distribution of $2p$ photoelectrons ejected from the ${2p}^{6}3p{}_{}{}^2{}_{}{}^{}P_{3/2}^{}{}_{}{}^{}$ state of excited sodium atoms have been performed over a broad photon energy range (50–140 eV) using synchrotron radiation. The outgoing photoelectrons were detected with a new multichannel system. The angular distribution of these electrons was also calculated in the $R$-matrix approximation. Our theoretical results for the partial photoionization cross sections and the angular distribution parameter are in excellent agreement with all experimental observations reported here and in earlier works.