Highly selective population of spin-orbit levels in electronic autoionization ofO2

The dynamics of electronic autoionization in ${\mathrm{O}}_2$ has been studied using a new apparatus which combines a free-jet supersonic expansion with synchrotron radiation. Ions and electrons were analyzed by a double time-of-flight spectrometer. The spin-orbit sublevels of the ${}_{}{}^3{}_{}{}^{}\mathrm{\Pi }_{\mathrm{u}}^{}{}_{}{}^{}$ (v=0 and 2) Rydberg states in ${\mathrm{O}}_2$ were selectively excited and the resulting ${\mathrm{O}}_2^{+}$ final states were determined by time-of-flight photoelectron spectros copy. A strong variation of the ${}_{}{}^2{}_{}{}^{}\mathrm{\Pi }_{1/2\mathrm{}\mathit{g}}^{}{}_{}{}^{}$ ${:}^2$ ${\mathrm{\Pi }}_{3/2\mathrm{}\mathit{g}}$ branching ratio was observed. This variation results from the selection of a single continuum wave function in the autoionization process.