Electron Correlation Effects in Photoemission from the1πuLevel in Acetylene

The photoemission cross section for the $1{\pi }_{\mathrm{u}}$ level in acetylene is calculated including electronic correlations using a time-dependent local-density approximation. Structure in the cross section from 12 to 17 eV is identified as arising from a Fano autoionization resonance ($2{\sigma }_{\mathrm{u}}\to 1{\pi }_{\mathrm{g}}$) and a redistribution of oscillator strength from a bound-to-bound transition ($1{\pi }_{\mathrm{u}}\to 1{\pi }_{\mathrm{g}}$) to the continuum. A minimum in the observed photoemission asymmetry parameter and the optical frequency polarizability are also accounted for with electronic correlations.