Measurements and calculations of high-angular-momentum satellite transitions in Li1sphotoionization

Abstract

Lithium $1s$ photoelectron spectra are reported in high electron and photon energy resolution, with resolved LS term structure of the ${\mathrm{Li}}^{+}$ $1snl$ satellite transitions up to $n=6.$ Branching ratios and anisotropy parameters of individual lines, determined over the 85--130 eV photon energy range, are compared with R-matrix calculations and with previous works. The high-angular-momentum satellite lines $(L>~2)$ are found to contribute significantly to the $1snl$ satellite cross sections for $n=3$ and 4, and to become the dominant terms for $n>~5.$ The high-angular-momentum lines exhibit the same photon-energy-dependence as the P-lines, providing experimental evidence that the continuum-continuum state coupling (equivalent to virtual electron collision processes) is responsible for the $L>~1$ terms in the satellite spectrum, in contrast to the electron relaxation (shake-up) mechanism responsible for the S-terms. The angular distribution of the lines in the ${\mathrm{Li}}^{+}$ $1snl,$ $n=2--6$ groups, determined at 110 eV photon energy, is in good agreement with calculations, showing more isotropic distributions for high-angular-momentum lines.